Ordered sets for high-speed interconnects

ABSTRACT

A system and apparatus can include a port for transmitting data; and a link coupled to the port. The port can include a physical layer device (PHY) to decode a physical layer packet, the physical layer packet received across the link. The physical layer packet can include a first bit sequence corresponding to a first ordered set, and a second bit sequence corresponding to a second ordered set, the first bit sequence immediately adjacent to the second bit sequence. The first ordered set is received at a predetermined ordered set interval, which can occur following a flow control unit (flit). The first ordered set comprises eight bytes and the second ordered set comprises eight bytes. In embodiments, bit errors in the ordered sets can be determined by checking bits received against expected bits for the ordered set interval.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation (and claims the benefit of priorityunder 35 U.S.C. § 120) of U.S. application Ser. No. 16/723,868, filedDec. 20, 2019, and entitled “ORDERED SETS FOR HIGH-SPEED INTERCONNECTS,”which application claims the benefit of U.S. Provisional PatentApplication having Ser. No. 62/846,913, filed on May 13, 2019, andentitled “ERROR PROTECTION FOR ORDERED SETS IN COMPUTER BUSES.” Thedisclosures of the prior applications are considered part of and arehereby incorporated by reference in their entirety in the disclosure ofthis application.

BACKGROUND

Ordered sets are physical layer packets that can be used by interconnectlink partners for various control functionality. For example, orderedsets can be used for link training, power management, flow control, andother physical layer functions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a block diagram for a computingsystem including a multicore processor.

FIG. 2A is a schematic diagram of an interlinked system that includestwo retimers in accordance with embodiments of the present disclosure.

FIG. 2B is a schematic diagram of a connected system that illustratesin-band upstream port and retimer configuration in accordance withembodiments of the present disclosure.

FIG. 3A is a schematic diagram illustrating example electric idleordered sets in accordance with embodiments of the present disclosure.

FIG. 3B is a schematic diagram illustrating example electric idle exitordered sets in accordance with embodiments of the present disclosure.

FIG. 3C is a schematic diagram illustrating example skip ordered sets inaccordance with embodiments of the present disclosure.

FIG. 4 is a process flow diagram for processing ordered sets inaccordance with embodiments of the present disclosure.

FIG. 5 is a schematic diagram illustrating example start data streamordered sets in accordance with embodiments of the present disclosure.

FIG. 6A is a schematic diagram illustrating example ordered sets forwaking from a low power state in accordance with embodiments of thepresent disclosure.

FIG. 6B is a process flow diagram for processing ordered sets for wakingfrom a low power state in accordance with embodiments of the presentdisclosure.

FIG. 7 illustrates an embodiment of a computing system including aninterconnect architecture.

FIG. 8 illustrates an embodiment of an interconnect architectureincluding a layered stack.

FIG. 9 illustrates an embodiment of a request or packet to be generatedor received within an interconnect architecture.

FIG. 10 illustrates an embodiment of a transmitter and receiver pair foran interconnect architecture.

FIG. 11 illustrates another embodiment of a block diagram for acomputing system including a processor.

FIG. 12 illustrates an embodiment of a block for a computing systemincluding multiple processor sockets.

FIG. 13 illustrates an exemplary flit definition with a per-lane FECscheme for a x4 PCIe link.

FIG. 14 illustrates exemplary flit definitions with a per-lane FECscheme for x8 and x2 PCIe links.

FIG. 15 shows a table of flit characteristics for exemplary flitdefinitions with per-lane FEC schemes for various PCIe link widths.

FIGS. 16A-16C illustrate exemplary flit packet sequences according tovarious placement rules.

FIG. 17 shows a table of PCIe 5.0 TLP efficiencies.

FIG. 18A is a schematic diagram of an example pair of protocol stacksimplemented in a transmitting-receiving device pair in accordance withembodiments of the present disclosure.

FIG. 18B is a schematic diagram of an example logical PHY that includeslogical elements for encoding and decoding ordered sets in accordancewith embodiments of the present disclosure.

Figures are not drawn to scale.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth,such as examples of specific types of processors and systemconfigurations, specific hardware structures, specific architectural andmicro architectural details, specific register configurations, specificinstruction types, specific system components, specificmeasurements/heights, specific processor pipeline stages and operationetc. in order to provide a thorough understanding of the presentdisclosure. It will be apparent, however, to one skilled in the art thatthese specific details need not be employed to practice the presentdisclosure. In other instances, well known components or methods, suchas specific and alternative processor architectures, specific logiccircuits/code for described algorithms, specific firmware code, specificinterconnect operation, specific logic configurations, specificmanufacturing techniques and materials, specific compilerimplementations, specific expression of algorithms in code, specificpower down and gating techniques/logic and other specific operationaldetails of computer system haven't been described in detail in order toavoid unnecessarily obscuring the present disclosure.

Although the following embodiments may be described with reference toenergy conservation and energy efficiency in specific integratedcircuits, such as in computing platforms or microprocessors, otherembodiments are applicable to other types of integrated circuits andlogic devices. Similar techniques and teachings of embodiments describedherein may be applied to other types of circuits or semiconductordevices that may also benefit from better energy efficiency and energyconservation. For example, the disclosed embodiments are not limited todesktop computer systems or Ultrabooks™. And may be also used in otherdevices, such as handheld devices, tablets, other thin notebooks,systems on a chip (SOC) devices, and embedded applications. Someexamples of handheld devices include cellular phones, Internet protocoldevices, digital cameras, personal digital assistants (PDAs), andhandheld PCs. Embedded applications typically include a microcontroller,a digital signal processor (DSP), a system on a chip, network computers(NetPC), set-top boxes, network hubs, wide area network (WAN) switches,or any other system that can perform the functions and operations taughtbelow. Moreover, the apparatus', methods, and systems described hereinare not limited to physical computing devices, but may also relate tosoftware optimizations for energy conservation and efficiency. As willbecome readily apparent in the description below, the embodiments ofmethods, apparatus', and systems described herein (whether in referenceto hardware, firmware, software, or a combination thereof) are vital toa ‘green technology’ future balanced with performance considerations.

As computing systems are advancing, the components therein are becomingmore complex. As a result, the interconnect architecture to couple andcommunicate between the components is also increasing in complexity toensure bandwidth requirements are met for optimal component operation.Furthermore, different market segments demand different aspects ofinterconnect architectures to suit the market's needs. For example,servers require higher performance, while the mobile ecosystem issometimes able to sacrifice overall performance for power savings. Yet,it's a singular purpose of most fabrics to provide highest possibleperformance with maximum power saving. Below, a number of interconnectsare discussed, which would potentially benefit from aspects of thedisclosure described herein.

Referring to FIG. 1, an embodiment of a block diagram for a computingsystem including a multicore processor is depicted. Processor 100includes any processor or processing device, such as a microprocessor,an embedded processor, a digital signal processor (DSP), a networkprocessor, a handheld processor, an application processor, aco-processor, a system on a chip (SOC), or other device to execute code.Processor 100, in one embodiment, includes at least two cores-core 101and 102, which may include asymmetric cores or symmetric cores (theillustrated embodiment). However, processor 100 may include any numberof processing elements that may be symmetric or asymmetric.

In one embodiment, a processing element refers to hardware or logic tosupport a software thread. Examples of hardware processing elementsinclude: a thread unit, a thread slot, a thread, a process unit, acontext, a context unit, a logical processor, a hardware thread, a core,and/or any other element, which is capable of holding a state for aprocessor, such as an execution state or architectural state. In otherwords, a processing element, in one embodiment, refers to any hardwarecapable of being independently associated with code, such as a softwarethread, operating system, application, or other code. A physicalprocessor (or processor socket) typically refers to an integratedcircuit, which potentially includes any number of other processingelements, such as cores or hardware threads.

A core often refers to logic located on an integrated circuit capable ofmaintaining an independent architectural state, wherein eachindependently maintained architectural state is associated with at leastsome dedicated execution resources. In contrast to cores, a hardwarethread typically refers to any logic located on an integrated circuitcapable of maintaining an independent architectural state, wherein theindependently maintained architectural states share access to executionresources. As can be seen, when certain resources are shared and othersare dedicated to an architectural state, the line between thenomenclature of a hardware thread and core overlaps. Yet often, a coreand a hardware thread are viewed by an operating system as individuallogical processors, where the operating system is able to individuallyschedule operations on each logical processor.

Physical processor 100, as illustrated in FIG. 1, includes twocores-core 101 and 102. Here, core 101 and 102 are considered symmetriccores, i.e. cores with the same configurations, functional units, and/orlogic. In another embodiment, core 101 includes an out-of-orderprocessor core, while core 102 includes an in-order processor core.However, cores 101 and 102 may be individually selected from any type ofcore, such as a native core, a software managed core, a core adapted toexecute a native Instruction Set Architecture (ISA), a core adapted toexecute a translated Instruction Set Architecture (ISA), a co-designedcore, or other known core. In a heterogeneous core environment (i.e.asymmetric cores), some form of translation, such a binary translation,may be utilized to schedule or execute code on one or both cores. Yet tofurther the discussion, the functional units illustrated in core 101 aredescribed in further detail below, as the units in core 102 operate in asimilar manner in the depicted embodiment.

As depicted, core 101 includes two hardware threads 101 a and 101 b,which may also be referred to as hardware thread slots 101 a and 101 b.Therefore, software entities, such as an operating system, in oneembodiment potentially view processor 100 as four separate processors,i.e., four logical processors or processing elements capable ofexecuting four software threads concurrently. As alluded to above, afirst thread is associated with architecture state registers 101 a, asecond thread is associated with architecture state registers 101 b, athird thread may be associated with architecture state registers 102 a,and a fourth thread may be associated with architecture state registers102 b. Here, each of the architecture state registers (101 a, 101 b, 102a, and 102 b) may be referred to as processing elements, thread slots,or thread units, as described above. As illustrated, architecture stateregisters 101 a are replicated in architecture state registers 101 b, soindividual architecture states/contexts are capable of being stored forlogical processor 101 a and logical processor 101 b. In core 101, othersmaller resources, such as instruction pointers and renaming logic inallocator and renamer block 130 may also be replicated for threads 101 aand 101 b. Some resources, such as re-order buffers inreorder/retirement unit 135, ILTB 120, load/store buffers, and queuesmay be shared through partitioning. Other resources, such as generalpurpose internal registers, page-table base register(s), low-leveldata-cache and data-TLB 115, execution unit(s) 140, and portions ofout-of-order unit 135 are potentially fully shared.

Processor 100 often includes other resources, which may be fully shared,shared through partitioning, or dedicated by/to processing elements. InFIG. 1, an embodiment of a purely exemplary processor with illustrativelogical units/resources of a processor is illustrated. Note that aprocessor may include, or omit, any of these functional units, as wellas include any other known functional units, logic, or firmware notdepicted. As illustrated, core 101 includes a simplified, representativeout-of-order (OOO) processor core. But an in-order processor may beutilized in different embodiments. The OOO core includes a branch targetbuffer 120 to predict branches to be executed/taken and aninstruction-translation buffer (I-TLB) 120 to store address translationentries for instructions.

Core 101 further includes decode module 125 coupled to fetch unit 120 todecode fetched elements. Fetch logic, in one embodiment, includesindividual sequencers associated with thread slots 101 a, 101 b,respectively. Usually core 101 is associated with a first ISA, whichdefines/specifies instructions executable on processor 100. Oftenmachine code instructions that are part of the first ISA include aportion of the instruction (referred to as an opcode), whichreferences/specifies an instruction or operation to be performed. Decodelogic 125 includes circuitry that recognizes these instructions fromtheir opcodes and passes the decoded instructions on in the pipeline forprocessing as defined by the first ISA. For example, as discussed inmore detail below decoders 125, in one embodiment, include logicdesigned or adapted to recognize specific instructions, such astransactional instruction. As a result of the recognition by decoders125, the architecture or core 101 takes specific, predefined actions toperform tasks associated with the appropriate instruction. It isimportant to note that any of the tasks, blocks, operations, and methodsdescribed herein may be performed in response to a single or multipleinstructions; some of which may be new or old instructions. Notedecoders 126, in one embodiment, recognize the same ISA (or a subsetthereof). Alternatively, in a heterogeneous core environment, decoders126 recognize a second ISA (either a subset of the first ISA or adistinct ISA).

In one example, allocator and renamer block 130 includes an allocator toreserve resources, such as register files to store instructionprocessing results. However, threads 101 a and 101 b are potentiallycapable of out-of-order execution, where allocator and renamer block 130also reserves other resources, such as reorder buffers to trackinstruction results. Unit 130 may also include a register renamer torename program/instruction reference registers to other registersinternal to processor 100. Reorder/retirement unit 135 includescomponents, such as the reorder buffers mentioned above, load buffers,and store buffers, to support out-of-order execution and later in-orderretirement of instructions executed out-of-order.

Scheduler and execution unit(s) block 140, in one embodiment, includes ascheduler unit to schedule instructions/operation on execution units.For example, a floating point instruction is scheduled on a port of anexecution unit that has an available floating point execution unit.Register files associated with the execution units are also included tostore information instruction processing results. Exemplary executionunits include a floating point execution unit, an integer executionunit, a jump execution unit, a load execution unit, a store executionunit, and other known execution units.

Lower level data cache and data translation buffer (D-TLB) 150 arecoupled to execution unit(s) 140. The data cache is to store recentlyused/operated on elements, such as data operands, which are potentiallyheld in memory coherency states. The D-TLB is to store recentvirtual/linear to physical address translations. As a specific example,a processor may include a page table structure to break physical memoryinto a plurality of virtual pages.

Here, cores 101 and 102 share access to higher-level or further-outcache, such as a second level cache associated with on-chip interface110. Note that higher-level or further-out refers to cache levelsincreasing or getting further way from the execution unit(s). In oneembodiment, higher-level cache is a last-level data cache—last cache inthe memory hierarchy on processor 100—such as a second or third leveldata cache. However, higher level cache is not so limited, as it may beassociated with or includes an instruction cache. A trace cache—a typeof instruction cache—instead may be coupled after decoder 125 to storerecently decoded traces. Here, an instruction potentially refers to amacro-instruction (i.e. a general instruction recognized by thedecoders), which may decode into a number of micro-instructions(micro-operations).

In the depicted configuration, processor 100 also includes on-chipinterface module 110. Historically, a memory controller, which isdescribed in more detail below, has been included in a computing systemexternal to processor 100. In this scenario, on-chip interface 110 is tocommunicate with devices external to processor 100, such as systemmemory 175, a chipset (often including a memory controller hub toconnect to memory 175 and an I/O controller hub to connect peripheraldevices), a memory controller hub, a northbridge, or other integratedcircuit. And in this scenario, bus 105 may include any knowninterconnect, such as multi-drop bus, a point-to-point interconnect, aserial interconnect, a parallel bus, a coherent (e.g. cache coherent)bus, a layered protocol architecture, a differential bus, and a GTL bus.

Memory 175 may be dedicated to processor 100 or shared with otherdevices in a system. Common examples of types of memory 175 includeDRAM, SRAM, non-volatile memory (NV memory), and other known storagedevices. Note that device 180 may include a graphic accelerator,processor or card coupled to a memory controller hub, data storagecoupled to an I/O controller hub, a wireless transceiver, a flashdevice, an audio controller, a network controller, or other knowndevice.

Recently however, as more logic and devices are being integrated on asingle die, such as SOC, each of these devices may be incorporated onprocessor 100. For example in one embodiment, a memory controller hub ison the same package and/or die with processor 100. Here, a portion ofthe core (an on-core portion) 110 includes one or more controller(s) forinterfacing with other devices such as memory 175 or a graphics device180. The configuration including an interconnect and controllers forinterfacing with such devices is often referred to as an on-core (orun-core configuration). As an example, on-chip interface 110 includes aring interconnect for on-chip communication and a high-speed serialpoint-to-point Link 105 for off-chip communication. Yet, in the SOCenvironment, even more devices, such as the network interface,co-processors, memory 175, graphics processor 180, and any other knowncomputer devices/interface may be integrated on a single die orintegrated circuit to provide small form factor with high functionalityand low power consumption.

In one embodiment, processor 100 is capable of executing a compiler,optimization, and/or translator code 177 to compile, translate, and/oroptimize application code 176 to support the apparatus and methodsdescribed herein or to interface therewith. A compiler often includes aprogram or set of programs to translate source text/code into targettext/code. Usually, compilation of program/application code with acompiler is done in multiple phases and passes to transform hi-levelprogramming language code into low-level machine or assembly languagecode. Yet, single pass compilers may still be utilized for simplecompilation. A compiler may utilize any known compilation techniques andperform any known compiler operations, such as lexical analysis,preprocessing, parsing, semantic analysis, code generation, codetransformation, and code optimization.

Larger compilers often include multiple phases, but most often thesephases are included within two general phases: (1) a front-end, i.e.generally where syntactic processing, semantic processing, and sometransformation/optimization may take place, and (2) a back-end, i.e.generally where analysis, transformations, optimizations, and codegeneration takes place. Some compilers refer to a middle, whichillustrates the blurring of delineation between a front-end and back endof a compiler. As a result, reference to insertion, association,generation, or other operation of a compiler may take place in any ofthe aforementioned phases or passes, as well as any other known phasesor passes of a compiler. As an illustrative example, a compilerpotentially inserts operations, calls, functions, etc. in one or morephases of compilation, such as insertion of calls/operations in afront-end phase of compilation and then transformation of thecalls/operations into lower-level code during a transformation phase.Note that during dynamic compilation, compiler code or dynamicoptimization code may insert such operations/calls, as well as optimizethe code for execution during runtime. As a specific illustrativeexample, binary code (already compiled code) may be dynamicallyoptimized during runtime. Here, the program code may include the dynamicoptimization code, the binary code, or a combination thereof.

The following detailed description refers to the accompanying drawings.The same reference numbers may be used in different drawings to identifythe same or similar elements. In the following description, for purposesof explanation and not limitation, specific details are set forth suchas particular structures, architectures, interfaces, techniques, etc. inorder to provide a thorough understanding of the various aspects ofvarious embodiments. However, it will be apparent to those skilled inthe art having the benefit of the present disclosure that the variousaspects of the various embodiments may be practiced in other examplesthat depart from these specific details. In certain instances,descriptions of well-known devices, circuits, and methods are omitted soas not to obscure the description of the various embodiments withunnecessary detail.

FIG. 2A is a schematic and timing diagram illustrating a sample topology200 with two re-timers 204 and 206 between an upstream componentdownstream port 202 and a downstream component upstream port 208 inaccordance with embodiments of the present disclosure. The upstreamcomponent downstream port 202 can be a port for a PCIe-based device,such as a CPU or other device capable of generating a data packet andtransmitting the data packet across a data Link compliant with the PCIeprotocol. The downstream component upstream port 208 can be a port for aperipheral component that can receive a data packet from a Linkcompliant with the PCIe protocol. It is understood that the upstreamcomponent downstream port 202 and the downstream component upstream port208 can transmit and receive data packets across PCIe Link(s),illustrated as PCIe Link 210 a-c.

The topology 200 can include one or more retimers 204 and 206. Retimers204 and 206 can serve as a signal repeater operating at the physicallayer to fine tune the signal from the upstream component 202 and/or thedownstream component upstream port 208. A retimer can use ContinuousTime Linear Equalization (CTLE), Decision Feedback Equalization (DFE),and transmit an impulse response equalization (Tx FIR EQ, orjust TxEQ).Re-timers are transparent to the data Link and transaction layers butimplement the full physical layer.

The multi-Lane PCIe Link is split into three Link segments (LS) 210 a,210 b, and 210 c in each direction. The upstream component downstreamport 202 can be coupled to retimer1 204 by a multi-Lane PCIe Link 210 a.The retimer 1 204 can be coupled to retimer 2 206 by link segment 210 b.And retimer 2 206 can be coupled to downstream component upstream port208 by link segment 210 c.

Components can also be coupled by sideband linkages. The upstreamcomponent downstream port 202 can be coupled to retimer1 204 by asideband link 212 a. The retimer 1 204 can be coupled to retimer 2 206by sideband link 212 b. And retimer 2 206 can be coupled to downstreamcomponent upstream port 208 by sideband link 212 c.

A primary function of a retimer (buffer) device is signal re-timing.These functions are performed by retimers 204 and 206. The particularretimer device circuits will depend on the PHY being used for the link.Generally, retimer circuitry is configured to recover the incomingsignal and retransmit using a local clock and new transmit equalizationcircuitry, and may typically employ well-known circuitry for thispurpose, such as phase lock loops. A retimer may further comprisetransmitter and receiver circuitry including one or more amplifiercircuits, as well as various types of well-known signal-conditioningcircuitry used to increase the drive level of a received signal. Suchretimer circuitry is well-known to those skilled in the high-speedinterconnect arts, and, accordingly, no further details are shown ordiscussed herein.

Each retimer 204 and 206 can have an upstream path and a downstreampath. In some implementations, a retimer can include two pseudo ports,and the pseudo ports can determine their respective downstream/upstreamorientation dynamically. Further, retimers 204 and 206 can supportoperating modes including a forwarding mode and an executing mode.Retimers 204 and 206 in some instances can decode data received on thesub-link and re-encode the data that it is to forward downstream on itsother sublink. As such, retimers may capture the received bit streamprior to regenerating and re-transmitting the bit stream to anotherdevice or even another retimer (or redriver or repeater). In some cases,the retimer can modify some values in the data it receives, such as whenprocessing and forwarding ordered set data. Additionally, a retimer canpotentially support any width option as its maximum width, such as a setof width options defined by a specification such as PCIe.

As data rates of serial interconnects (e.g., PCIe, UPI, USB, etc.)increase, retimers are increasingly used to extend the channel reach.Multiple retimers can be cascaded for even longer channel reach. It isexpected that as signal speeds increase, channel reach will typicallydecrease as a general matter. Accordingly, as interconnect technologiesaccelerate, the use of retimers may become more common. As an example,as PCIe Gen-4, with its 16 GT/s, is adopted in favor of PCIe Gen-3 (8GT/s), the use of retimers in PCIe interconnects may increase, as may bethe case in other interconnects as speeds increase.

In one implementation, a common BGA (Ball Grid Array) footprint may bedefined for PCI Express Gen-4 (16 GT/s) based retimers. Such a designmay address at least some of the example shortcomings found inconventional PCIe Gen-3 (8 GT/s) retimer devices, as well as some of theissues emerging with the adoption of PCIe Gen-4. Further, for PCIeGen-4, the number of retimer vendors and volume are expected toincrease. Due to signal losses from the doubled data rate (from 8 GT/sto 16 GT/s), the interconnect length achievable is significantlydecreased in Gen-4. In this and other example interconnect technologies,as data rate increases, retimers may thereby have increased utility asthey can be used to dramatically increase channel lengths that would beotherwise constrained by the increased data rate.

Although shown to be separate from the upstream component and downstreamcomponent, the retimer can be part of the upstream or downstreamcomponents, on board with the upstream or downstream components, or onpackage with the downstream component.

The upstream component downstream port 202 can have access to a storageelement 222, such as a flash storage, cache, or other memory device. Theretimer 1 204 can optionally include a similar storage element 224. Theretimer 2 206 can optionally include a similar storage element 226. Thedownstream component upstream port 208 can optionally include a similarstorage element 228.

FIG. 2B is a schematic diagram of a connected system 250 thatillustrates in-band upstream port and retimer configuration inaccordance with embodiments of the present disclosure. As shown in FIG.2A, an upstream component downstream port 202 can be coupled to thedownstream component upstream port 208 by a link 210 a-c that isextended by two retimers 204, 206. In this example, the downstream port202 can be provided with a retimer configuration register address/dataregister 252 to hold data to be sent in a configuration access commandto one of the two retimers using fields of an enhanced SKP OS. One ormore bits of the SKP OS can include a command code, data, or an addressfor use at a configuration register (e.g., 256, 258) of a retimer (e.g.,204, 206, respectively) to read or write data from/to the register 256,258. Retimers can respond to configuration access commands sent byencoding data in an instance of an enhanced SKP OS by itself encodingresponse data in a subsequent instance of an enhanced SKP OS. Dataencoded by the retimer (e.g., 204, 206) may be extracted at thedownstream port and recorded in a retimer configuration data returnregister (e.g., 254). The registers (e.g., 252, 254) maintained at theupstream device downstream port 202 can be written to and read from bysystem software and/or other components of the system allowing(indirect) access to the retimer registers: one register (e.g., 252)conveying the address/data/command to the retimer and a second register(e.g., 254) that stores the responses coming back from the re-timer. Inother implementations, such registers (e.g., 260) can be maintained atthe downstream component upstream port 208 instead of or in addition tothe registers being maintained at the upstream component downstream port202, among other examples.

Continuing with the example of FIG. 2B, in connection with a mechanismfor providing in-band access to retimer registers, the retimer may havearchitected registers that are addressable with well-defined bits andcharacteristics. In this example, an enhanced SKP OS is defined/modifiedas the physical layer-generated periodic pattern to carry thecommands/information from “Retimer Config Reg Addr/Data” (e.g., 252) tothe re-timers and carrying the responses from the re-timers back to loadto “Retimer Config Data Return” (e.g., 840), with some bits allotted forCRC for the protection of data. For example, in PCIe this can includeenhancing the existing SKP Ordered Set (e.g., with CSR Access and CSRReturn (CRC-protected bits)). Further, a flow for ensuring guaranteeddelivery of the commands/information to retimer and the correspondingresponse back can be defined. The physical layer mechanism can beenhanced to also include notifications from the re-timer (in addition toresponse) if it needs some sort of service, among other examplesfeatures.

PCIe Generation 6 and beyond can use Pulse Amplitude Modulation (PAM-4)with forward error correction (FEC) to run at 64 GT/s at an effectiveBit Error Rate (BER) for the data stream in an acceptable range. FEC andflits for data blocks for data blocks are often used for normaloperations when the Link is in an active (L0) power state.

Ordered Sets (OS), however, cannot be protected by the same FECmechanism because many, if not most, OS are not scrambled. For example,Electrical Idle Exit Ordered Sets (EIEOS) are used to reset thescrambler, provide a low-frequency pattern, and obtain block alignment.So EIEOS are not scrambled and should not be changed with errorcorrecting code (ECC) bits. Skip Ordered Sets (SKP OS) can be ofvariable length as SKP OS can be added or deleted by Retimers.Therefore, using FEC to cover all Ordered Sets is challenging, each OSwith its own unique set of requirements and length. This disclosuredescribes error protection mechanisms for Ordered Sets in a high-BERInterconnect Link, such as a link based on a PCIe Gen 6 or aboveprotocol, while preserving the characteristics and functionalityassociated with each Ordered Set.

In this disclosure, a physical layer device can partition a 128b OS intotwo 64-b (8B) portions or chunks. Replicated along with CRC/parityprotection is used for improved reliability and availability.

Ordered sets fall into two broad categories each with a differentapproach for high raw BER:

An Ordered Set such as TS1/TS2 is considered good if either an 8B chunkis good, each of which is independently CRC protected.

An Ordered Set such as SKP OS (creates or removes delay between linkpartners), EIEOS (retraining), EIOS (lower power state) sent after aData Stream, need both 8B chunks to be good to be considered a good OS.Therefore, each 8B chunk has its own built-in redundancy to improve itseffective BER.

Control SKP Ordered Set payload such as Parity and margin command/statusfields will be sent in a predetermined flit in lieu of the data linklayer payload to avoid aliasing in the Ordered Sets due to the high rawBER in the Link.

The techniques and devices described herein result in preserving theexisting PCIe Ordered Set mechanisms while providing reliability andavailability with a high BER expected in Gen 6.

This disclosure defines each Ordered Set (OS) to be a 128 bit (16 Byte)block. Each 128 bit OS block includes two 64 bit (8B) chunks orportions. This apportioning is done to handle a fault model where eachburst is of length <=16. If the burst length is longer, the sameprinciples apply by making the Ordered Set longer. For example, if theburst length is <=32, each OS can be 256 bits comprising of two 128 bitchunks. Table 1 illustrates effective bit error rates (BER) achievedusing OS apportioning.

TABLE 1 Effective bit error rates (BER) achieved using OS apportioning.Gen 1-5 Gen 6 Raw burst    1E−12 0.0001 0.00001 0.000001   1E−7   1E−8  1E−9 error probability OS basic 130  64 64 64 64 64 64 sizeProbability of error 0  1 0.993620118 0.99936 0.999936 0.999994 99999940.99999994 1  1.3E−10 0.006359805 0.00064  6.4E−5 6.4E−6  6.4E−7  6.4E−82 8.385E−21 2.00354E−5 2.01E−7  2.02E−9 2.02E−11 2.016E−13 2.016E−15 33.5776E− 4.14106E−8 4.16E−11  4.17E−14 4.17E−17 4.166E−20 4.1664E−23  31Prob of >=1  1.3E−10 0.006379882 0.00064 6.4E−5 6.4E−6  6.4E−7  6.4E−8error in OS basic size (no single error correct) Prob of >=2 2.00768E−52.02E−7  2.02E−9 2.02E−11 2.016E−13 2.016E−15 errors in OS basic size(single error correct) Error prob 4.07029E−5 4.09E−7   4.1E−9  4.1E−114.096E−13 4.096E−15 when OS needs either of two 8B all correct (TS1/TS2)Error prob  4.03078E−10 4.06E−14 4.06E−18 4.06E−22 4.064E−26 4.0643E−30 when both 8B needed to be correct but need 5B in each 8B

Each OS falls into two broad categories; each with a different approachfor handling high raw BER using the two 8B chunks:

An Ordered Set such as TS1/TS2 is considered good if either 8B chunk isgood, each of which is independently CRC protected.

An Ordered Set such as SKP OS, EIEOS, EIOS sent after a Data Stream,need both 8B chunks to be good to be considered a good OS. However, each8B chunk has its own built-in redundancy to improve its effective BER.

These replication across two 8B chunks or within each 8B chunk helps theOS to have the same effective error probability of 1.3E-10 in most ofthe cases, as shown in Table 1 below. There are some cases (e.g.,TS1/TS2 with a raw BER of 1E-4) where the number falls short. Those canbe addressed by replication across Ordered Sets (e.g., send 24 TS2Ordered Sets instead of 16 TS2 Ordered Sets in PCIe Gen 1-5).

In this disclosure, the sync header that distinguishes between an OS(128b) vs a Data Block is not used. Instead, SKP Ordered Sets are sentat a fixed interval. Once a Data Stream starts, SKP Ordered Setcontinues at that fixed interval. However, a SKP OS can be substitutedby an Electrical Idle Exit Ordered Set (EIEOS) if the Link needs totransition from an active state (L0) to Recovery; the SKP OS can besubstituted for an Electrical Idle Ordered Set (EIOS) if the Link needsto transition to a low-power state such as L0s or L1 from L0. Thus,while in a data stream, a Receiver can be configured to recognize one ofthe 3 OS: SKP OS, EIEOS, or EIOS during certain intervals. During that16B aligned block, the Receiver can distinguish between one of the threeOS, assuming the burst length it is supposed to correct.

FIG. 3A is a schematic diagram illustrating example electric idleordered sets (EIOS) 300 in accordance with embodiments of the presentdisclosure. The EIOS 300 is shown as 16 bytes (or two 8 byte portions302 and 304). Redundancy is also shown, where each 8B portion isrepeated. FIG. 3B is a schematic diagram illustrating example electricidle exit ordered sets 310 in accordance with embodiments of the presentdisclosure. The EIEOS 310 is shown as 16 bytes (or two 8 byte portions312 and 314). Redundancy is also shown, where each 8B portion isrepeated.

FIG. 3C is a schematic diagram illustrating example skip ordered sets320 in accordance with embodiments of the present disclosure. FIG. 3Cillustrates SKP OS 322 as an 8B portion, and with other SKP OS portions324. In embodiments, 24-48B of SKP OS can be used. SKP_END OS 326 canrepresent the end of the SKP OS, and can also be portioned into 8Bportions. The PHY payload 328 can be scheduled after the SKP_END OS 326.The PHY Payload can also be replicated in a similar manner as other OSfor redundancy. That is, the PHY payload can be apportioned into two 8byte portions, with each of the 8 byte portions carrying the sameinformation.

FIGS. 3A-C illustrates example encoding for the three Ordered Sets thatcan be received immediately after a Data Block, at the scheduled SKP OSinterval. The EIEOS 300 is chosen to preserve the 1 GHz low-frequencycontent. The EIOS and SKP OS are chosen to have a reasonable hammingdistance between the 4B aligned encodings between EIOS 300, EIEOS 310,and SKP/SKP_END OS 320, as shown in Table 2 below. Those skilled in theart will recognize that this will prevent any aliasing with a bursterror of <=16. The values shown in Table 2, along with the respectivehamming distances, can be used as expected values against which receivedOS can be compared. One or both of the redundant OS received can bechecked against expected values to determined OS type and whether thereceived OS contains errors.

TABLE 2 Encoding differences between various OS. Comparison (aligned 4B)Difference SKP vs SKP_END 0FFF_F0FF SKP/SKP_END vs EIOSFFFF_FFFF/F000_0F00 SKP/SKP_END vs EIEOS F00F_F00F/FFF0_00F0 (all 0s vsall Fs in first 8B vs the last 8B) (0FF0_0FF0/000F_FF0F)

FIG. 4 is a process flow diagram 400 for processing ordered sets inaccordance with embodiments of the present disclosure. The process flowchart 400 demonstrates the techniques described herein for identifyingthe appropriate Ordered Set, even in the presence of errors, and takingthe appropriate action.

In this disclosure, SKP Ordered Sets arrive at a receiver at a regularinterval, as described later. During a data stream 402, the receiverskips checking for OS 406 if the received data is outside the SKP OSinterval 404.

During a data stream 402, at the interval where an OS (such as a SKP OS)is expected 404, the receiver distinguishes between the three OS thatcan show up in that position. The receiver checks for 5 out of 8 Bytesmatching with the corresponding Byte position (408), (410). This checkensures any error affecting up to 3 Bytes (a burst of length <=16 willimpact at most 3 Bytes) can be corrected and will result in a match. Ifno match is found, it implies more errors, and the Link enters Recovery,to retrain the Link (412). If 5 of 8 bytes match (410), then thereceiver can determine an OS type between SKP OS, EIOS, and EIEOS (414).Receiving an EIOS indicates that the Link will enter a low-power state(L0s, L1) after the next 8 Bytes (428). Receiving an EIEOS puts the Linkto Recovery (412).

If the receiver receives a SKP OS after having read the first 8B (416),the receiver continues to check the next 8 Bytes for either a SKP or aSKP_END (418). If 5 out of 8 Bytes match an expected SKP_END OS, itindicates the Data Stream after the 8 Bytes of PHY payload at the end ofthe SKP OS. The PHY payload can be processed (422) and the receiverreturns to checking for OS during scheduled OS intervals (404).

A received SKP OS can be 24, 32, 40, 48, or 56 Bytes long. So that check(for a SKP or a SKP_END) can happen for up to 5 times, if the receivercontinues receiving SKP OS. If at least 5 of the 8 Bytes match SKP OS(424), the receiver can check that the number of 8B SKP OS received doesnot exceed 5. If the number of 8B SKP OS is greater than or equal to 6(exceeds 5), the link can enter recovery (412). If at least 5 of the 8Bytes do not match SKP OS (424), then the link enters recovery (412). Ifneither SKP nor SKP_END OS is found or the SKP vs SKP_END OS check hasalready happened 5 times and the receiver has been receiving acontinuous stream of SKP OS, the Link enters Recovery since it indicatesan uncorrectable error.

If the number of SKP or SKP_END does not exceed 5, the receiver can readthe next 8B (418) and continue from there to check SKP OS or SKP_END OS.

In this disclosure, SKP OS are inserted at a fixed intervals. This ischosen to be aligned to flow control unit (flit) boundary. During a Datastream, a SKP OS can be inserted at a flit boundary or inserted within aTLP in progress which straddles two (or more) flits.

Each Retimer can insert or delete two SKPs (i.e., 8 Bytes). A SKP OStransmitted by a Port can be 40 Bytes, but when received at a Port, theSKP OS can be 24, 32, 40, 48, or 56 Bytes. Since 8 Bytes are added ordeleted in each Port/Pseudo-Port, the SKP OS insertion interval can bemade twice as long as PCIe Gen 3-5 (i.e., 740 Blocks for SRNS or CommonClock and 74 Blocks for SRIS, where 1 Block=16 Bytes per Lane).

In Gen 4 and Gen 5 Data Rates, Control SKP Ordered Set was used forpayload such as Parity and margin command/status fields. In Gen 3through Gen 5 Data Rates, SKP OS carried parity information to identifythe Lane segment in error along with the LFSR (Linear Feedback ShiftRegister) value for that Lane. Control SKP OS and SKP OS alternate inGen 4 and Gen 5 Data Rates. With a burst error expected in a high BERLink, the techniques described herein append the this information in thelast 8 Bytes of the SKP OS interval with replication, as shown in Table3.

TABLE 3 PHY layer payload at the end of the SKP OS. PHY Payload BitField 0 Payload Type: [32]       Margin Payload if 0b; else LFSR 1, 2, 3Parity bits (Port parity, Retimer 1 Parity, Retimer 2 Parity) [33, 34,35] 4:27 {LFSR[2:0], Margin Payload, Margin CRC, Margin Parity} ifMargin payload [36:59]    Else {Parity of LFSR[22:0], LFSR[22:0]} 28Payload Type [60]       Margin Payload if 0b; else LFSR 29, 30, 31Parity bits (port parity, Retimer 1 Parity, Retimer 2 Parity) [61, 62,63]

Despite one type of SKP OS being used, the Payload alternates betweenlinear feedback shift register (LFSR) sequences and MarginCommand/Status, similar to Gen 4 and Gen 5. The “Payload Type” fieldindicates what type of payload is sent and is replicated 4 times.Similarly, the Port Parity, reflecting the even parity of all the bitsin the previous flits starting from after the SDS OS or the prior SKPOS, whichever earlier, to the flit before the current SKP OS, along with2 bits reflecting each Retimer's computation of parity is sent 4 times.The Payload Type along with the three parity bits are replicated 4times. A majority voting is employed across all this 4-bit vector todetermine which one is correct. The LFSR is sent two times along withits corresponding even parity and compared to deploy the correct one.The Margin Payload along with the Margin CRC/parity is sent twice. Ifone set of the two copies passes its parity and CRC check, it will beused as a valid copy.

Link (Re)Training is handled through the TS1/TS2 Ordered Sets with theEIEOS sent every 32 TS1/TS2 Ordered Sets. Link (re)training occurs inRecovery and Configuration states. If the Link was in Electrical Idleprior to entering Recovery, the EIEOS is used to wake up the LinkPartner. This disclosure will send 4 back to back EIEOS followed by 32TS1 Ordered Sets in a repeating pattern. The 4 back to back EIEOS issent to ensure that a low-frequency pattern (of 0.5 GHz) stays for 8 nsfor the exit electrical idle (EI) detection circuitry of the LinkPartner to wave up. Once the Link Partner wakes up, as evidenced byrecording an exit EI signal (and optionally some progress inestablishing bit lock), the Link can send one EIEOS every 32 TS1/TS2Ordered Sets to minimize the link (re)training time. The TS1/TS2 OrderedSet carries a lot of information bits. However, not all the informationbits are required in all the states. Since the Link has a high BER, theproposed invention splits each TS1/TS2 Ordered Set (16 Symbols, eachSymbol being a Byte) into two identical halves, as shown in Table 4below. Symbol 0 (and 8) is the TS1 identifier, which is unscrambled. Theinformation bits that do not need to overlap in each of the states aresent on the same Symbol. For example, Link Number and Lane Number ismeaningful in states like Configuration—not in Recovery. Equalizationinformation (denoted as EQ Bytes 0-3) are useful only in Recovery states(and mostly in Recovery.EQ sub-state)—so they are sent during thosestates. So Symbol 1 and 2 EQ Bytes in Recovery states but carry LinkNo/Lane No in other states, as shown in Table 4 below. This helps tosend the relevant information more often within the same number of Bytesto effectively correct errors. Each 7 Bytes is protected by an 8-bit CRCwhich is sent in Symbol 8/15. It should be noted that since identicalSymbols are 8 Bytes apart, a burst error <=64 bits will not impact thecopy. The only OS that can coexist during (re)training are TS1/TS2,EIEOS, and SKP OS.

TABLE 4 TS1/TS2 Ordered Sets. Symbol No Field/State ScrambledUsage/Value 0, 8  TS1/TS2 Identifier No 1 Eh/2 Dh 1, 9  LinkNo-non-Recovery states Yes EQ Byte 0-Recovery 2, 10 Lane No-non-Recoverystates Yes EQ Byte 1-Recovery 3, 11 NFTS Yes 4, 12 Data Rate IdentifierYes 5, 13 EQ Byte 2 Yes 6, 14 Training Control-in non-Recovery.EQsubstates Yes EQ Byte 3-Recovery.EQ 7, 15 8b CRC over Symbols 0-6 (or8-14) OR Yes/No 8 bit CRC OR DC-balance [or byte parity] DC Balance: 20h or DFh

FIG. 5 is a schematic diagram illustrating example start data streamordered sets 500 in accordance with embodiments of the presentdisclosure. The start data stream (SDS) OS provide markers prior to thebeginning of the data stream. The SDS OS indicate an end of TS2.Therefore, the start of SDS OS an also indicate the end of TS2 OS. Thebuilt-in redundancy of SDS OS is shown by 8B portion 502 and 8B portion504.

FIG. 6A is a schematic diagram illustrating example ordered sets forwaking from a low power state in accordance with embodiments of thepresent disclosure. FIG. 6B is a process flow diagram for processingordered sets for waking from a low power state in accordance withembodiments of the present disclosure. A receiver can be in a low powerstate (e.g., a L0s state) (652). On exit from a low-power state, thetechniques described herein follows the sequence shown in FIGS. 6A-B. Atthe outset, an initial 4 EIEOS can cause the receiver of a link partnerto wake up from the low power state (654). Following that, the N fasttraining sequence (FST) gets the receiver to achieve bit lock (656). Insome embodiments, TS1/TS2 OS can be used instead of the N FST. Then,EIEOS (1-4 OS) can be used to achieve block alignment (658). Followingblock alignment, a SKP OS sequence (40 Bytes) can be used to establishthe SKP interval (660) and perform Lane to Lane Deskew (662). TheSKP/SKP_END OS are checked using 5 good bytes in an 8 Byte alignedboundary and the SDS is accepted as long as at least four goodE1_87_87_87 (4B) sets in 4B aligned boundary are received over the 32Bytes of SDS (as described by FIG. 4). The SDS marks the beginning of anew Data Stream (664). The SDS can also be used to establish lane tolane deskew.

This disclosure describes the following rules during training forbuilt-in error correction with reliability:

A received TS1/TS2 is considered valid as long as Symbols 0-7 or Symbols8-15 pass CRC/parity check. If both sets pass CRC/parity but do notmatch each other, the one that matches a prior TS1/TS2, if any, isaccepted as valid. If there are no prior TS1/TS2 and both the setsmismatch, we can accept either one as the valid TS1/TS2.

An EIEOS can be used to obtain block alignment prior to decipheringTS1/TS2 Ordered Sets. The block boundary is updated if a subsequentEIEOS is on a different boundary.

The SKP OS can be received and initial checks can be stringent to matchall Bytes for the SKP and SKP_END (instead of the 5 out of 8 Bytesmatch). A SKP OS interval can be established with at least two SKP OSprior to sending TS2 Ordered Sets.

Two back to back SDS can be sent prior to starting the Data Stream,neither of which should overlap with the location of the start of theSKP OS at the Transmitter.

An SDS is considered “received” in an aligned 128b (16B) boundary if:

1) the SDS is not the location of a SKP OS starting point;

2) the receiver has received the mandatory number of TS2′es per LTSSMrules;

3) the receiver has received four good E1_87_87_87 (4B) sets, at leasttwo of which is in an odd 4B aligned position (i.e. Bytes 0-3, 8-11).(This third rule ensures that the receiver checks directly against thefixed TS2 unscrambled bytes; EIEOS is checked naturally since it isunscrambled in all bytes, in a similar way as the SDS).

A Receiver can receive two SDS back to back to start receiving the DataStream.

Even though the disclosure is described in the context of PCIe Gen 6,those skilled in the art will realize that the concepts are applicableto other interconnects (such as future generations of multi-Lane Linkssuch as coherency/memory links, USB, etc.) if OS are used.

One interconnect fabric architecture includes the Peripheral ComponentInterconnect (PCI) Express (PCIe) architecture. A primary goal of PCIeis to enable components and devices from different vendors tointer-operate in an open architecture, spanning multiple marketsegments; Clients (Desktops and Mobile), Servers (Standard andEnterprise), and Embedded and Communication devices. PCI Express is ahigh performance, general purpose I/O interconnect defined for a widevariety of future computing and communication platforms. Some PCIattributes, such as its usage model, load-store architecture, andsoftware interfaces, have been maintained through its revisions, whereasprevious parallel bus implementations have been replaced by a highlyscalable, fully serial interface. The more recent versions of PCIExpress take advantage of advances in point-to-point interconnects,Switch-based technology, and packetized protocol to deliver new levelsof performance and features. Power Management, Quality Of Service (QoS),Hot-Plug/Hot-Swap support, Data Integrity, and Error Handling are amongsome of the advanced features supported by PCI Express.

Referring to FIG. 7, an embodiment of a fabric composed ofpoint-to-point Links that interconnect a set of components isillustrated. System 700 includes processor 705 and system memory 710coupled to controller hub 715. Processor 705 includes any processingelement, such as a microprocessor, a host processor, an embeddedprocessor, a co-processor, or other processor. Processor 705 is coupledto controller hub 715 through front-side bus (FSB) 706. In oneembodiment, FSB 706 is a serial point-to-point interconnect as describedbelow. In another embodiment, link 706 includes a serial, differentialinterconnect architecture that is compliant with different interconnectstandard.

System memory 710 includes any memory device, such as random accessmemory (RAM), non-volatile (NV) memory, or other memory accessible bydevices in system 700. System memory 710 is coupled to controller hub715 through memory interface 716. Examples of a memory interface includea double-data rate (DDR) memory interface, a dual-channel DDR memoryinterface, and a dynamic RAM (DRAM) memory interface.

In one embodiment, controller hub 715 is a root hub, root complex, orroot controller in a Peripheral Component Interconnect Express (PCIe orPCIE) interconnection hierarchy. Examples of controller hub 715 includea chipset, a memory controller hub (MCH), a northbridge, an interconnectcontroller hub (ICH) a southbridge, and a root port controller/hub.Often the term chipset refers to two physically separate controllerhubs, i.e. a memory controller hub (MCH) coupled to an interconnectcontroller hub (ICH). Note that current systems often include the MCHintegrated with processor 705, while controller 715 is to communicatewith I/O devices, in a similar manner as described below. In someembodiments, peer-to-peer routing is optionally supported through rootcomplex 715.

Here, controller hub 715 is coupled to switch/bridge 720 through seriallink 719. Input/output modules 717 and 721, which may also be referredto as interfaces/ports 717 and 721, include/implement a layered protocolstack to provide communication between controller hub 715 and switch720. In one embodiment, multiple devices are capable of being coupled toswitch 720.

Switch/bridge 720 routes packets/messages from device 725 upstream, i.e.up a hierarchy towards a root complex, to controller hub 715 anddownstream, i.e. down a hierarchy away from a root port controller, fromprocessor 705 or system memory 710 to device 725. Switch 720, in oneembodiment, is referred to as a logical assembly of multiple virtualPCI-to-PCI bridge devices. Device 725 includes any internal or externaldevice or component to be coupled to an electronic system, such as anI/O device, a Network Interface Controller (NIC), an add-in card, anaudio processor, a network processor, a hard-drive, a storage device, aCD/DVD ROM, a monitor, a printer, a mouse, a keyboard, a router, aportable storage device, a Firewire device, a Universal Serial Bus (USB)device, a scanner, and other input/output devices. Often in the PCIevernacular, such as device, is referred to as an endpoint. Although notspecifically shown, device 725 may include a PCIe to PCI/PCI-X bridge tosupport legacy or other version PCI devices. Endpoint devices in PCIeare often classified as legacy, PCIe, or root complex integratedendpoints.

Graphics accelerator 730 is also coupled to controller hub 715 throughserial link 732. In one embodiment, graphics accelerator 730 is coupledto an MCH, which is coupled to an ICH. Switch 720, and accordingly I/Odevice 725, is then coupled to the ICH. I/O modules 731 and 718 are alsoto implement a layered protocol stack to communicate between graphicsaccelerator 730 and controller hub 715. Similar to the MCH discussionabove, a graphics controller or the graphics accelerator 730 itself maybe integrated in processor 705.

Turning to FIG. 8 an embodiment of a layered protocol stack isillustrated. Layered protocol stack 700 includes any form of a layeredcommunication stack, such as a Quick Path Interconnect (QPI) stack, aPCIe stack, a next generation high performance computing interconnectstack, or other layered stack. Although the discussion immediately belowin reference to FIGS. 7-10 are in relation to a PCIe stack, the sameconcepts may be applied to other interconnect stacks. In one embodiment,protocol stack 800 is a PCIe protocol stack including transaction layer805, link layer 810, and physical layer 820. An interface, such asinterfaces 717, 718, 721, 722, 726, and 731 in FIG. 7, may berepresented as communication protocol stack 800. Representation as acommunication protocol stack may also be referred to as a module orinterface implementing/including a protocol stack.

PCI Express uses packets to communicate information between components.Packets are formed in the Transaction Layer 805 and Data Link Layer 810to carry the information from the transmitting component to thereceiving component. As the transmitted packets flow through the otherlayers, they are extended with additional information necessary tohandle packets at those layers. At the receiving side the reverseprocess occurs and packets get transformed from their Physical Layer 820representation to the Data Link Layer 810 representation and finally(for Transaction Layer Packets) to the form that can be processed by theTransaction Layer 705 of the receiving device.

Transaction Layer

In one embodiment, transaction layer 805 is to provide an interfacebetween a device's processing core and the interconnect architecture,such as data link layer 810 and physical layer 820. In this regard, aprimary responsibility of the transaction layer 805 is the assembly anddisassembly of packets (i.e., transaction layer packets, or TLPs). Thetranslation layer 805 typically manages credit-base flow control forTLPs. PCIe implements split transactions, i.e. transactions with requestand response separated by time, allowing a link to carry other trafficwhile the target device gathers data for the response.

In addition PCIe utilizes credit-based flow control. In this scheme, adevice advertises an initial amount of credit for each of the receivebuffers in Transaction Layer 805. An external device at the opposite endof the link, such as controller hub 715 in FIG. 7, counts the number ofcredits consumed by each TLP. A transaction may be transmitted if thetransaction does not exceed a credit limit. Upon receiving a response anamount of credit is restored. An advantage of a credit scheme is thatthe latency of credit return does not affect performance, provided thatthe credit limit is not encountered.

In one embodiment, four transaction address spaces include aconfiguration address space, a memory address space, an input/outputaddress space, and a message address space. Memory space transactionsinclude one or more of read requests and write requests to transfer datato/from a memory-mapped location. In one embodiment, memory spacetransactions are capable of using two different address formats, e.g., ashort address format, such as a 32-bit address, or a long addressformat, such as 64-bit address. Configuration space transactions areused to access configuration space of the PCIe devices. Transactions tothe configuration space include read requests and write requests.Message space transactions (or, simply messages) are defined to supportin-band communication between PCIe agents.

Therefore, in one embodiment, transaction layer 805 assembles packetheader/payload 706. Format for current packet headers/payloads may befound in the PCIe specification at the PCIe specification website.

Quickly referring to FIG. 9, an embodiment of a PCIe transactiondescriptor is illustrated. In one embodiment, transaction descriptor 900is a mechanism for carrying transaction information. In this regard,transaction descriptor 900 supports identification of transactions in asystem. Other potential uses include tracking modifications of defaulttransaction ordering and association of transaction with channels.

Transaction descriptor 900 includes global identifier field 902,attributes field 904, and channel identifier field 906. In theillustrated example, global identifier field 902 is depicted comprisinglocal transaction identifier field 908 and source identifier field 910.In one embodiment, global transaction identifier 902 is unique for alloutstanding requests.

According to one implementation, local transaction identifier field 908is a field generated by a requesting agent, and it is unique for alloutstanding requests that require a completion for that requestingagent. Furthermore, in this example, source identifier 810 uniquelyidentifies the requestor agent within a PCIe hierarchy. Accordingly,together with source ID 910, local transaction identifier 908 fieldprovides global identification of a transaction within a hierarchydomain.

Attributes field 904 specifies characteristics and relationships of thetransaction. In this regard, attributes field 904 is potentially used toprovide additional information that allows modification of the defaulthandling of transactions. In one embodiment, attributes field 904includes priority field 912, reserved field 914, ordering field 916, andno-snoop field 918. Here, priority sub-field 912 may be modified by aninitiator to assign a priority to the transaction. Reserved attributefield 914 is left reserved for future, or vendor-defined usage. Possibleusage models using priority or security attributes may be implementedusing the reserved attribute field.

In this example, ordering attribute field 916 is used to supply optionalinformation conveying the type of ordering that may modify defaultordering rules. According to one example implementation, an orderingattribute of “0” denotes default ordering rules are to apply, wherein anordering attribute of “1” denotes relaxed ordering, wherein writes canpass writes in the same direction, and read completions can pass writesin the same direction. Snoop attribute field 918 is utilized todetermine if transactions are snooped. As shown, channel ID Field 906identifies a channel that a transaction is associated with.

Link Layer

Link layer 810, also referred to as data link layer 810, acts as anintermediate stage between transaction layer 805 and the physical layer820. In one embodiment, a responsibility of the data link layer 810 isproviding a reliable mechanism for exchanging Transaction Layer Packets(TLPs) between two components a link. One side of the Data Link Layer810 accepts TLPs assembled by the Transaction Layer 805, applies packetsequence identifier 811, i.e. an identification number or packet number,calculates and applies an error detection code, i.e. CRC 812, andsubmits the modified TLPs to the Physical Layer 820 for transmissionacross a physical to an external device.

Physical Layer

In one embodiment, physical layer 820 includes logical sub block 821 andelectrical sub-block 822 to physically transmit a packet to an externaldevice. Here, logical sub-block 821 is responsible for the “digital”functions of Physical Layer 821. In this regard, the logical sub-blockincludes a transmit section to prepare outgoing information fortransmission by physical sub-block 822, and a receiver section toidentify and prepare received information before passing it to the LinkLayer 810.

Physical block 822 includes a transmitter and a receiver. Thetransmitter is supplied by logical sub-block 821 with symbols, which thetransmitter serializes and transmits onto to an external device. Thereceiver is supplied with serialized symbols from an external device andtransforms the received signals into a bit-stream. The bit-stream isde-serialized and supplied to logical sub-block 821. In one embodiment,an 8b/10b transmission code is employed, where ten-bit symbols aretransmitted/received. Here, special symbols are used to frame a packetwith frames 823. In addition, in one example, the receiver also providesa symbol clock recovered from the incoming serial stream.

As stated above, although transaction layer 805, link layer 810, andphysical layer 820 are discussed in reference to a specific embodimentof a PCIe protocol stack, a layered protocol stack is not so limited. Infact, any layered protocol may be included/implemented. As an example,an port/interface that is represented as a layered protocol includes:(1) a first layer to assemble packets, i.e. a transaction layer; asecond layer to sequence packets, i.e. a link layer; and a third layerto transmit the packets, i.e. a physical layer. As a specific example, acommon standard interface (CSI) layered protocol is utilized.

Referring next to FIG. 10, an embodiment of a PCIe serial point to pointfabric is illustrated. Although an embodiment of a PCIe serialpoint-to-point link is illustrated, a serial point-to-point link is notso limited, as it includes any transmission path for transmitting serialdata. In the embodiment shown, a basic PCIe link includes two,low-voltage, differentially driven signal pairs: a transmit pair1006/1011 and a receive pair 1012/1007. Accordingly, device 1005includes transmission logic 1006 to transmit data to device 1010 andreceiving logic 1007 to receive data from device 1010. In other words,two transmitting paths, i.e. paths 1016 and 1017, and two receivingpaths, i.e. paths 1018 and 1019, are included in a PCIe link.

A transmission path refers to any path for transmitting data, such as atransmission line, a copper line, an optical line, a wirelesscommunication channel, an infrared communication link, or othercommunication path. A connection between two devices, such as device1005 and device 1010, is referred to as a link, such as link 1015. Alink may support one lane—each lane representing a set of differentialsignal pairs (one pair for transmission, one pair for reception). Toscale bandwidth, a link may aggregate multiple lanes denoted by xN,where N is any supported Link width, such as 1, 2, 4, 8, 12, 16, 32, 64,or wider.

A differential pair refers to two transmission paths, such as lines 1016and 1017, to transmit differential signals. As an example, when line1016 toggles from a low voltage level to a high voltage level, i.e. arising edge, line 1017 drives from a high logic level to a low logiclevel, i.e. a falling edge. Differential signals potentially demonstratebetter electrical characteristics, such as better signal integrity, i.e.cross-coupling, voltage overshoot/undershoot, ringing, etc. This allowsfor better timing window, which enables faster transmission frequencies.

Note that the apparatus, methods, and systems described above may beimplemented in any electronic device or system as aforementioned. Asspecific illustrations, the figures below provide exemplary systems forutilizing the disclosure as described herein. As the systems below aredescribed in more detail, a number of different interconnects aredisclosed, described, and revisited from the discussion above. And as isreadily apparent, the advances described above may be applied to any ofthose interconnects, fabrics, or architectures.

Turning to FIG. 11, a block diagram of an exemplary computer systemformed with a processor that includes execution units to execute aninstruction, where one or more of the interconnects implement one ormore features in accordance with one embodiment of the presentdisclosure is illustrated. System 1100 includes a component, such as aprocessor 1102 to employ execution units including logic to performalgorithms for process data, in accordance with the present disclosure,such as in the embodiment described herein. System 1100 isrepresentative of processing systems based on the PENTIUM III™, PENTIUM4™, Xeon™ Itanium, XScale™ and/or StrongARM™ microprocessors availablefrom Intel Corporation of Santa Clara, Calif., although other systems(including PCs having other microprocessors, engineering workstations,set-top boxes and the like) may also be used. In one embodiment, samplesystem 1000 executes a version of the WINDOWS™ operating systemavailable from Microsoft Corporation of Redmond, Wash., although otheroperating systems (UNIX and Linux for example), embedded software,and/or graphical user interfaces, may also be used. Thus, embodiments ofthe present disclosure are not limited to any specific combination ofhardware circuitry and software.

Embodiments are not limited to computer systems. Alternative embodimentsof the present disclosure can be used in other devices such as handhelddevices and embedded applications. Some examples of handheld devicesinclude cellular phones, Internet Protocol devices, digital cameras,personal digital assistants (PDAs), and handheld PCs. Embeddedapplications can include a micro controller, a digital signal processor(DSP), system on a chip, network computers (NetPC), set-top boxes,network hubs, wide area network (WAN) switches, or any other system thatcan perform one or more instructions in accordance with at least oneembodiment.

In this illustrated embodiment, processor 1102 includes one or moreexecution units 1008 to implement an algorithm that is to perform atleast one instruction. One embodiment may be described in the context ofa single processor desktop or server system, but alternative embodimentsmay be included in a multiprocessor system. System 1100 is an example ofa ‘hub’ system architecture. The computer system 1100 includes aprocessor 1102 to process data signals. The processor 1102, as oneillustrative example, includes a complex instruction set computer (CISC)microprocessor, a reduced instruction set computing (RISC)microprocessor, a very long instruction word (VLIW) microprocessor, aprocessor implementing a combination of instruction sets, or any otherprocessor device, such as a digital signal processor, for example. Theprocessor 1102 is coupled to a processor bus 1110 that transmits datasignals between the processor 1102 and other components in the system1100. The elements of system 1100 (e.g. graphics accelerator 1112,memory controller hub 1116, memory 1120, I/O controller hub 1124,wireless transceiver 1126, Flash BIOS 1028, Network controller 1134,Audio controller 1136, Serial expansion port 1138, I/O controller 1140,etc.) perform their conventional functions that are well known to thosefamiliar with the art.

In one embodiment, the processor 1102 includes a Level 1 (L1) internalcache memory 1104. Depending on the architecture, the processor 1102 mayhave a single internal cache or multiple levels of internal caches.Other embodiments include a combination of both internal and externalcaches depending on the particular implementation and needs. Registerfile 1106 is to store different types of data in various registersincluding integer registers, floating point registers, vector registers,banked registers, shadow registers, checkpoint registers, statusregisters, and instruction pointer register.

Execution unit 1108, including logic to perform integer and floatingpoint operations, also resides in the processor 1102. The processor1102, in one embodiment, includes a microcode (ucode) ROM to storemicrocode, which when executed, is to perform algorithms for certainmacroinstructions or handle complex scenarios. Here, microcode ispotentially updateable to handle logic bugs/fixes for processor 1102.For one embodiment, execution unit 1108 includes logic to handle apacked instruction set 1109. By including the packed instruction set1109 in the instruction set of a general-purpose processor 1102, alongwith associated circuitry to execute the instructions, the operationsused by many multimedia applications may be performed using packed datain a general-purpose processor 1102. Thus, many multimedia applicationsare accelerated and executed more efficiently by using the full width ofa processor's data bus for performing operations on packed data. Thispotentially eliminates the need to transfer smaller units of data acrossthe processor's data bus to perform one or more operations, one dataelement at a time.

Alternate embodiments of an execution unit 1108 may also be used inmicro controllers, embedded processors, graphics devices, DSPs, andother types of logic circuits. System 1100 includes a memory 1120.Memory 1020 includes a dynamic random access memory (DRAM) device, astatic random access memory (SRAM) device, flash memory device, or othermemory device. Memory 1120 stores instructions and/or data representedby data signals that are to be executed by the processor 1102.

Note that any of the aforementioned features or aspects of thedisclosure may be utilized on one or more interconnect illustrated inFIG. 11. For example, an on-die interconnect (ODI), which is not shown,for coupling internal units of processor 1102 implements one or moreaspects of the disclosure described above. Or the disclosure isassociated with a processor bus 1110 (e.g. Intel Quick Path Interconnect(QPI) or other known high performance computing interconnect), a highbandwidth memory path 1118 to memory 1120, a point-to-point link tographics accelerator 1112 (e.g. a Peripheral Component Interconnectexpress (PCIe) compliant fabric), a controller hub interconnect 1122, anI/O or other interconnect (e.g. USB, PCI, PCIe) for coupling the otherillustrated components. Some examples of such components include theaudio controller 1136, firmware hub (flash BIOS) 1128, wirelesstransceiver 1126, data storage 1124, legacy I/O controller 1110containing user input and keyboard interfaces 1142, a serial expansionport 1138 such as Universal Serial Bus (USB), and a network controller1134. The data storage device 1124 can comprise a hard disk drive, afloppy disk drive, a CD-ROM device, a flash memory device, or other massstorage device.

Referring now to FIG. 12, shown is a block diagram of a second system1200 in accordance with an embodiment of the present disclosure. Asshown in FIG. 12, multiprocessor system 1200 is a point-to-pointinterconnect system, and includes a first processor 1270 and a secondprocessor 1280 coupled via a point-to-point interconnect 1250. Each ofprocessors 1270 and 1280 may be some version of a processor. In oneembodiment, 1252 and 1254 are part of a serial, point-to-point coherentinterconnect fabric, such as Intel's Quick Path Interconnect (QPI)architecture. As a result, the disclosure may be implemented within theQPI architecture.

While shown with only two processors 1270, 1280, it is to be understoodthat the scope of the present disclosure is not so limited. In otherembodiments, one or more additional processors may be present in a givenprocessor.

Processors 1270 and 1280 are shown including integrated memorycontroller units 1272 and 1282, respectively. Processor 1270 alsoincludes as part of its bus controller units point-to-point (P-P)interfaces 1276 and 1278; similarly, second processor 1280 includes P-Pinterfaces 1286 and 1288. Processors 1270, 1280 may exchange informationvia a point-to-point (P-P) interface 1250 using P-P interface circuits1278, 1288. As shown in FIG. 12, IMCs 1272 and 1282 couple theprocessors to respective memories, namely a memory 1232 and a memory1234, which may be portions of main memory locally attached to therespective processors.

Processors 1270, 1280 each exchange information with a chipset 1290 viaindividual P-P interfaces 1252, 1254 using point to point interfacecircuits 1276, 1294, 1286, 1298. Chipset 1290 also exchanges informationwith a high-performance graphics circuit 1138 via an interface circuit1292 along a high-performance graphics interconnect 1239.

A shared cache (not shown) may be included in either processor oroutside of both processors; yet connected with the processors via P-Pinterconnect, such that either or both processors' local cacheinformation may be stored in the shared cache if a processor is placedinto a low power mode.

Chipset 1290 may be coupled to a first bus 1216 via an interface 1296.In one embodiment, first bus 1216 may be a Peripheral ComponentInterconnect (PCI) bus, or a bus such as a PCI Express bus or anotherthird generation I/O interconnect bus, although the scope of the presentdisclosure is not so limited.

As shown in FIG. 12, various I/O devices 1214 are coupled to first bus1216, along with a bus bridge 1218 which couples first bus 1216 to asecond bus 1220. In one embodiment, second bus 1220 includes a low pincount (LPC) bus. Various devices are coupled to second bus 1220including, for example, a keyboard and/or mouse 1222, communicationdevices 1227 and a storage unit 1228 such as a disk drive or other massstorage device which often includes instructions/code and data 1230, inone embodiment. Further, an audio I/O 1224 is shown coupled to secondbus 1220. Note that other architectures are possible, where the includedcomponents and interconnect architectures vary. For example, instead ofthe point-to-point architecture of FIG. 12, a system may implement amulti-drop bus or other such architecture.

Using the various inertial and environmental sensors present in aplatform, many different use cases may be realized. These use casesenable advanced computing operations including perceptual computing andalso allow for enhancements with regard to power management/batterylife, security, and system responsiveness.

For example with regard to power management/battery life issues, basedat least on part on information from an ambient light sensor, theambient light conditions in a location of the platform are determinedand intensity of the display controlled accordingly. Thus, powerconsumed in operating the display is reduced in certain lightconditions.

As to security operations, based on context information obtained fromthe sensors such as location information, it may be determined whether auser is allowed to access certain secure documents. For example, a usermay be permitted to access such documents at a work place or a homelocation. However, the user is prevented from accessing such documentswhen the platform is present at a public location. This determination,in one embodiment, is based on location information, e.g., determinedvia a GPS sensor or camera recognition of landmarks. Other securityoperations may include providing for pairing of devices within a closerange of each other, e.g., a portable platform as described herein and auser's desktop computer, mobile telephone or so forth. Certain sharing,in some implementations, are realized via near field communication whenthese devices are so paired. However, when the devices exceed a certainrange, such sharing may be disabled. Furthermore, when pairing aplatform as described herein and a smartphone, an alarm may beconfigured to be triggered when the devices move more than apredetermined distance from each other, when in a public location. Incontrast, when these paired devices are in a safe location, e.g., a workplace or home location, the devices may exceed this predetermined limitwithout triggering such alarm.

Responsiveness may also be enhanced using the sensor information. Forexample, even when a platform is in a low power state, the sensors maystill be enabled to run at a relatively low frequency. Accordingly, anychanges in a location of the platform, e.g., as determined by inertialsensors, GPS sensor, or so forth is determined. If no such changes havebeen registered, a faster connection to a previous wireless hub such asa Wi-Fi™ access point or similar wireless enabler occurs, as there is noneed to scan for available wireless network resources in this case.Thus, a greater level of responsiveness when waking from a low powerstate is achieved.

It is to be understood that many other use cases may be enabled usingsensor information obtained via the integrated sensors within a platformas described herein, and the above examples are only for purposes ofillustration. Using a system as described herein, a perceptual computingsystem may allow for the addition of alternative input modalities,including gesture recognition, and enable the system to sense useroperations and intent.

In some embodiments one or more infrared or other heat sensing elements,or any other element for sensing the presence or movement of a user maybe present. Such sensing elements may include multiple differentelements working together, working in sequence, or both. For example,sensing elements include elements that provide initial sensing, such aslight or sound projection, followed by sensing for gesture detection by,for example, an ultrasonic time of flight camera or a patterned lightcamera.

Also in some embodiments, the system includes a light generator toproduce an illuminated line. In some embodiments, this line provides avisual cue regarding a virtual boundary, namely an imaginary or virtuallocation in space, where action of the user to pass or break through thevirtual boundary or plane is interpreted as an intent to engage with thecomputing system. In some embodiments, the illuminated line may changecolors as the computing system transitions into different states withregard to the user. The illuminated line may be used to provide a visualcue for the user of a virtual boundary in space, and may be used by thesystem to determine transitions in state of the computer with regard tothe user, including determining when the user wishes to engage with thecomputer.

In some embodiments, the computer senses user position and operates tointerpret the movement of a hand of the user through the virtualboundary as a gesture indicating an intention of the user to engage withthe computer. In some embodiments, upon the user passing through thevirtual line or plane the light generated by the light generator maychange, thereby providing visual feedback to the user that the user hasentered an area for providing gestures to provide input to the computer.

Display screens may provide visual indications of transitions of stateof the computing system with regard to a user. In some embodiments, afirst screen is provided in a first state in which the presence of auser is sensed by the system, such as through use of one or more of thesensing elements.

In some implementations, the system acts to sense user identity, such asby facial recognition. Here, transition to a second screen may beprovided in a second state, in which the computing system has recognizedthe user identity, where this second the screen provides visual feedbackto the user that the user has transitioned into a new state. Transitionto a third screen may occur in a third state in which the user hasconfirmed recognition of the user.

In some embodiments, the computing system may use a transition mechanismto determine a location of a virtual boundary for a user, where thelocation of the virtual boundary may vary with user and context. Thecomputing system may generate a light, such as an illuminated line, toindicate the virtual boundary for engaging with the system. In someembodiments, the computing system may be in a waiting state, and thelight may be produced in a first color. The computing system may detectwhether the user has reached past the virtual boundary, such as bysensing the presence and movement of the user using sensing elements.

In some embodiments, if the user has been detected as having crossed thevirtual boundary (such as the hands of the user being closer to thecomputing system than the virtual boundary line), the computing systemmay transition to a state for receiving gesture inputs from the user,where a mechanism to indicate the transition may include the lightindicating the virtual boundary changing to a second color.

In some embodiments, the computing system may then determine whethergesture movement is detected. If gesture movement is detected, thecomputing system may proceed with a gesture recognition process, whichmay include the use of data from a gesture data library, which mayreside in memory in the computing device or may be otherwise accessed bythe computing device.

If a gesture of the user is recognized, the computing system may performa function in response to the input, and return to receive additionalgestures if the user is within the virtual boundary. In someembodiments, if the gesture is not recognized, the computing system maytransition into an error state, where a mechanism to indicate the errorstate may include the light indicating the virtual boundary changing toa third color, with the system returning to receive additional gesturesif the user is within the virtual boundary for engaging with thecomputing system.

As mentioned above, in other embodiments the system can be configured asa convertible tablet system that can be used in at least two differentmodes, a tablet mode and a notebook mode. The convertible system mayhave two panels, namely a display panel and a base panel such that inthe tablet mode the two panels are disposed in a stack on top of oneanother. In the tablet mode, the display panel faces outwardly and mayprovide touch screen functionality as found in conventional tablets. Inthe notebook mode, the two panels may be arranged in an open clamshellconfiguration.

In various embodiments, the accelerometer may be a 3-axis accelerometerhaving data rates of at least 50 Hz. A gyroscope may also be included,which can be a 3-axis gyroscope. In addition, an e-compass/magnetometermay be present. Also, one or more proximity sensors may be provided(e.g., for lid open to sense when a person is in proximity (or not) tothe system and adjust power/performance to extend battery life). Forsome OS's Sensor Fusion capability including the accelerometer,gyroscope, and compass may provide enhanced features. In addition, via asensor hub having a real-time clock (RTC), a wake from sensors mechanismmay be realized to receive sensor input when a remainder of the systemis in a low power state.

In some embodiments, an internal lid/display open switch or sensor toindicate when the lid is closed/open, and can be used to place thesystem into Connected Standby or automatically wake from ConnectedStandby state. Other system sensors can include ACPI sensors forinternal processor, memory, and skin temperature monitoring to enablechanges to processor and system operating states based on sensedparameters.

In an embodiment, the OS may be a Microsoft® Windows® 8 OS thatimplements Connected Standby (also referred to herein as Win8 CS).Windows 8 Connected Standby or another OS having a similar state canprovide, via a platform as described herein, very low ultra idle powerto enable applications to remain connected, e.g., to a cloud-basedlocation, at very low power consumption. The platform can supports 3power states, namely screen on (normal); Connected Standby (as a default“off” state); and shutdown (zero watts of power consumption). Thus inthe Connected Standby state, the platform is logically on (at minimalpower levels) even though the screen is off. In such a platform, powermanagement can be made to be transparent to applications and maintainconstant connectivity, in part due to offload technology to enable thelowest powered component to perform an operation.

FIG. 13 illustrates an exemplary flit definition with a per-lane FECscheme for a x4 PCIe link. A flit comprises one or more TLPs and DLLPsprotected by a flit-level CRC scheme and a per-lane FEC scheme. In someembodiments, a flit may be protected by a flit-level FEC scheme, as willdiscussed in greater detail below. Flit 1300 comprises transaction layerpacket symbols 1310, data link layer packet symbols 1320, flit-level CRCcode symbols 1330, and FEC symbols 1340. Flit 1300 comprises 324 totalsymbols. In some embodiments, a symbol can be 1 DW in length, but asymbol can be different lengths in other embodiments. The 324 symbols inflit 1300 comprise 288 symbols carrying transaction layer packetinformation (TL0-TL287), 4 symbols carrying data link layer packetinformation (DLL0-3), 8 flit-level CRC symbols (CRC0-7), and 24 FECsymbols (12 check symbols (C) and 12 parity symbols (P)). Eight CRCsymbols are used to ensure that multiple TL/DPP symbol errors arecovered adequately. Information from a single TLP can span multiple TLsymbols in a flit. For example, if a symbol is 1 DW long, flit 1350would need 8 TL symbols to store a TLP that is 8 DWs in length.

Flit 1300 is transmitted across lanes 1350 (L0-L3). That is, a differentportion of flit 1300 is sent across each of the four lanes. FIG. 13shows successive TL, DLL, and CRC symbols being transmitted alongadjacent lanes, but in other embodiments, symbols could be apportionedamong lanes in differing fashions.

Flit 1300 can have a flit sequence number, which may be specifiedexplicitly, implicitly, or opportunistically. If specified explicitly,the flit sequence number can be coded, for example, in reserved bits inthe flit. If specified implicitly, the flit sequence number may not besent across the link and a receiver can determine the flit packet numberin another fashion, such as, for example, by counting flits as they arereceived. If specified opportunistically, the flit sequence number canbe sent, for example, as payload in a DLLP packet that is sent in fullor in part as part of a flit. In one example of flit sequence numbersbeing sent implicitly, the CRC can include the flit sequence number as,for example, consecutive bits in the CRC code during CRC computation.Accordingly, any dropped or replayed flits could be detected at areceiving end.

In flit 1300, four one-byte symbols (DLL0-3) are allocated for one DLLP.In other embodiments, information from multiple DLLPs can be carried ina single flit. In still other embodiments, a DLLP can be constructedover consecutive flits. For example, in a flit format that allocatesfive DLLP bytes, four DLLP bytes can carry one DLLP and the fifth DLLPbyte from four consecutive flits can contribute to an additional DLLP.

The flit-level CRC code protects the flit contents minus the FEC checkand parity symbols. For example, the flit-level CRC codes in symbolsCRC0-7 in flit 1300 protect the TL, DLL and CRC symbols in flit 1300.The per-lane FEC scheme protects all symbols within a flit that aretransmitted across one lane. For example, the six FEC check and paritysymbols to be transmitted along one of the lanes L0-L3 protect the 81symbols (324 flit symbols/4 lanes) transmitted along that lane. The FECscheme further employs interleaving. The FEC scheme employed in flit1300 uses three-way interleaving, as represented by the shading of eachsymbol. For example, check and parity symbols 1360, shown with noshading, protect the symbols transmitted along lane L3 that are alsoshown with no shading (TL3, TL7, TL11 . . . TL287, CRC3, CRC7,check/parity symbols 1360). Thus, in the FEC scheme illustrated in FIG.13, two FEC symbols—one check symbol and one parity symbol—are used toprotect 27 flit symbols (81 symbols transmitted along lane L3/3-wayinterleaving). In other embodiments, alternative interleaving schemes(2-way, 4-way, etc.), as FEC schemes with more of fewer check and paritybits per lane can be used to achieve a desirable bit error rate.

Different flit definitions can be used for different link widths. FIG.14 illustrates exemplary flit definitions with per-lane FEC schemes forx8 and x2 PCIe links. Flit 1400 defines a 648-symbol flit format for aPCIe x8 link. Flit 1400 comprises 1400 symbols containing transactionlayer packet data (TL0-TL599), 4 symbols containing data link layerpacket data (DLL0-3), 8 flit-level CRC symbols (CRC0-7), and 48 FECsymbols (24 check symbols and 24 parity symbols). The 648 symbols aretransmitted across eight lanes (L0-L7). As in flit 1300, the six FECcheck and parity symbols transmitted in a lane protect 81 symbols (648symbols/8 lanes) using 3-way interleaving, with each pair of FEC checkand parity symbols protecting 27 symbols (81 symbols/3-wayinterleaving).

Flit 1450 is a 324-symbol flit definition for a PCIe x2 link. Flit 1450comprises 300 symbols carrying transaction layer packet information(TL0-TL299), 4 symbols carrying data link layer packet information(DLL0-3), eight CRC symbols (CRC0-7), and 12 FEC symbols (6 checksymbols and 6 parity symbols). The 324 symbols are transmitted acrosstwo lanes (L0-L1). The six FEC check and parity symbols transmitted ineach lane protect 162 symbols (324 symbols/2 lanes) using three-wayinterleaving, with each pair of FEC check and parity symbols protecting54 symbols (162 symbols/3-way interleaving).

Flits 1300, 1400 and 1450 show exemplary flit definitions for particularPCIe link widths. Other flit definitions are possible for a particularPCIe link. The number of TL and/or DLL symbols can vary from one flitdefinition to another, as can the number flit-level CRC symbols used toprotect a flit, the number of FEC symbols used to protect a lane, andthe degree of interleaving used for the FEC scheme. Increasing thenumber of flit-level CRC symbols and/or the FEC symbols used can reduceBER, but at the cost of increased overhead, and thus, efficiency.

In some embodiments, the flit definition for a particular link can bedefined, determined, or supplied by an operating system or BIOS duringsystem start-up. The flit definition for a link can be stored insoftware or firmware local to the system, be encoded in hardware, orstored remotely and accessed during system start-up. The flit definitionfor a particular link need not be static and can vary during systemoperation. For example, the physical layer, protocol stack, or operatingsystem can receive an updated flit definition for a particular link andthe link can begin using the updated flit definition at some point afterreceiving the updated flit definition. An updated flit definition can beprovided in response to various events. For example, a physical layercan monitor link performance and signal to the protocol stack oroperating system that the BER of the link is too high, and the systemcan switch to a flit definition that has a flit-level CRC scheme withmore CRC bytes, a per-lane FEC scheme that has more check and paritybits per lane, a flit-level FEC scheme that has more check and paritybits per flit, or a combination thereof. In another example, the systemcan determine that greater information throughput is possible whilekeeping the BER at an acceptable level and a flit definition providinggreater transmission efficiency can be used. Greater efficiency can beobtained in an updated flit definition by increasing the number ofTLP/DLLP packet symbols in the flit, or by reducing the number offlit-level CRC symbols and/or the number of FEC check/parity symbols.

FIG. 15 shows a table of flit characteristics for exemplary flitdefinitions with per-lane FEC schemes for various PCIe link widths.Table 1500 shows flit characteristics for flits 1300, 1400, and 1450 forx4, x8 and x2 links, respectively, and flit characteristics for possibleflit definitions for x1 and x16 links. The FEC latencies shown areapproximate latency times at transfer speeds proposed for PCIe Gen 6.The narrower links (x1, x2) have higher FEC latency to derive betterefficiency by amortizing the fixed overhead (flit-level CRC symbols anddata link layer packet information) as shown. Different flit sizes for agiven link width can be selected to trade-off latency for efficiency.

Flit-based packetization can provide at least the following advantages.First, flit-based packetization removes the need for a LCRC to beattached to each TLP since the flit is protected by a CRC scheme at theflit level. Flit 1300 in FIG. 13 comprises TLP data from 288 TLPs andonly eight flit-level CRC symbols. If sent across a link using currentPCIe protocols, those 288 TLPs would be accompanied by 288 LCRCs. Inother words, a flit does not contain a CRC sent along with each TLPincluded in the flit. With flit-based packetization, link layer retryhappens at the flit level. In one embodiment, a failed flit can beretried with a receiver storing successfully transmitted flits receivedat the receiver after the corrupted or missing flit. In someembodiments, a transmitter can be informed that a transmitted flit wasnot successfully received through receipt of a NAK DLLP containing thesequence number of the flit to be resent. In some embodiments, a retriedflit can indicate that it is being resent via a “retry flit” encoding inthe corresponding DLLP along with the sequence number of the retriedflit.

Second, flit-based packetization allows for the adoption of guaranteedDLLP frequency policies. In one embodiment, upon transmission of a flit,the transmitter is to receive a DLLP acknowledgment packet indicatingthat the flit was received no later than n flits after being sent. Inanother embodiment, a receiver is to send a DLLP packet providing creditupdates to the transmitter no later than m flits after accruing x numberof credits. Such policies can reduce storage overhead at the receiverrelative to current receiver storage needs, which account for currentPCIe DLLP scheduling policies and having to handle such situations assending an ACK or NAK DLLP behind a maximum payload size TLP.

Third, since flit definitions provide guaranteed positions for DLLPs ina flit, the 2-5% variable bandwidth loss due to DLLP scheduling isexchanged for a fixed bandwidth reduction for a given flit definition.For example, in the x4 flit definition of flit 1300, the bandwidthreduction due to DLLP overhead is only 1.2% (1/81).

Fourth, the bandwidth loss due to the addition of framing informationadded by the physical layer to each TLP is eliminated since transactionlayer packet information is in fixed locations in the flit and flitboundaries are known. That is, physical layer framing information is notadded to a TLP for every TLP transmitted as part of a flit.

Fifth, because a particular flit format has a defined length, thesynchronization header that is periodically sent in current PCIeprotocols can be replaced by a periodic ordered set (OS), such as a SKPOS (Skip Ordered Set), EIOS (Electrical Idle Ordered Set), or EIEOS(Electrical Idle Exit Ordered Set). In one embodiment, a periodic OS canbe sent every 72 flits for flits that are 10.25 ns long where there is a600-ppm clock spread. Replacing the synchronization header with aperiodic OS can reclaim at least a portion of the bandwidth consumedthrough use of a synchronization header. In current PCIe protocolformats, synchronization headers consume approximately 1.5% ofbandwidth.

FIGS. 16A-16C illustrate exemplary flit packet sequences according tovarious placement rules. A flit definition defines which slots or fieldsin the flit may be occupied by TLP or DLLP information, but, in someembodiments, placement or packing rules are used to determine where TLPor DLLP information for individual TLPs/DLLPs to be sent in a flit areplaced. FIGS. 16A-16C show a sequence of 48 flit packets transmittedacross a link. The packets are sent in order from left to right in eachrow, with the first row being sent first and the third row being sentlast. Each column is 1 DW wide and each set of four columns is 4 DWwide.

FIG. 16A illustrates TLPs placed in a flit according to the rule thatonly TLP header information or TLP payload (data) information can residein each aligned 4 DW set. Starting with the upper left-most packet, thefirst two 4 DW sets contain header information 1602 (h0-h3) and payloadinformation 1604 (d0-d3) of a first TLP. The next two 4 DW sets containNULL TLPs 1606 and 1608. The first 4 DW set in the second row containsheader information 1610 (h0-h2) for a second header-only TLP. Becausethe header of this second TLP is only 3 DWs wide, the fourth DW set isfilled with an IDL packet. Idle packets can be used to fill in 4 DW setswhere the header or payload information for a packet is less than fourDWs in length. Continuing along the second row, the second and third 4DW sets contain header information 1612 (h0-h2) and payload information1614 (d0) for a third TLP. Because the header and payload informationfor this third TLP is less than 4 DWs, the second and third 4 DW setsare filled with IDL packets. The fourth 4 DW set in the second row isfilled with header information 1616 (h0-h2) for a fourth TLP, and anidle packet. The payload 1618 (d0-d1) for the fourth TLP is placed inthe first two DWs of the third row, followed by two idle packets. Theremaining three 4 DW sets in the third row comprise header information1620 (h0-h2) for a fifth TLP, and header information 1622 (h0-h3) andpayload information 1624 (d0-d3) for a sixth TLP. In sum, six TLPs arepacked into the 48 DWs illustrated in FIG. 16A.

FIG. 16B illustrates TLPs and DLLPs placed in a flit according to therule that each aligned 4 DW set can contain header and data informationfrom one TLP, with DLLPs placed opportunistically. Starting with theupper left-most packet of FIG. 16B, the first two 4 DW sets containheader information 1642 (h0-h3) and payload information 1644 (d0-d3) ofa first TLP. The third 4 DW set contains NULL TLP 1646 and the fourth 4DW set contains a first DLLP 1648 followed by three IDL packets. Movingto the second row, the first 4 DW set contains header information 1650(h0-h2) for a second TLP, followed by an IDL packet. The second DWcontains header information 1652 (h0-h2) and payload information 1653(d0) for a third TLP. The first three DWs in the third 4 DW set in thesecond row is filled with header information 1654 (h0-h2) for a fourthTLP and an opportunistically placed second DLLP 1655. The fourth DW setin the second row contains payload information 1656 (d0-d1) for thefourth TLP, with the last two DWs containing idle packets. Continuing tothe last row, the first 4 DW set contains header information 1660(h0-h2) for a fifth TLP and an idle packet. The second and third 4 DWsets contain header information 1662 (h0-h3) and payload information1664 (d0-d3) for a sixth TLP. The last 4 DW set comprises headerinformation 1666 (h0-h2) and payload information 1667 (d0) for a seventhTLP. The first six TLPs placed in FIG. 16B are the same TLPs placed inFIG. 16A. The looser packing rules associated with FIG. 16B allow for aseventh TLP and two DLLPs to be additionally placed in the same 48 DWs.

FIG. 16C illustrates TLPs and DLLPs placed in a flit according to therule that TLP header and payload information can be placed at any DWboundary, with opportunistic DLLP placement. Placing the same 7 TLPs and2 DLLPs that were placed in FIG. 16B, the first TLP and the first DLLPare placed in the first row of FIG. 16C in the same manner as they werein FIG. 16B. Moving to the second row, the first 4 DW set containsinformation from the second and third TLPs: header 1690 (h0-h2) from thesecond TLP and the first DW (h0) of header information 1691 (h0-h2) ofthe third TLP. The remaining header information (h1-h2) of the third TLPis placed in the first two DWs of the second 4 DW set. Headerinformation 1693 (h0-h2) for a fourth DLP is contained in the last DW ofthe second 4 DW set and the first two DWs of the third 4 DW set. Thepayload information 1694 (d0-d1) of the fourth TLP is placed in thesecond half of the third 4 DW set. The last 4 DW set of the second rowcontains header information 1695 (h0-h2) of the fifth TLP. The headerinformation 1696 (h0-h3) of the sixth DLP fills the last DW of thesecond row and continues into the first three DWs of the first 4 DW setof the third row. The payload information 1697 (d0-d3) of the sixth TLPfills the last DW of the first 4 DW set in the third row and the firstthree DWs of the second 4 DW set. The remainder of the last row isfilled with the header information 1698 (h0-h2) and payload information1699 (d0) of the seventh TLP, a second DLLP 1681 and header information1683 (h0-h2) of an eighth TLP. Allowing TLP header and payload data tobe placed in any DW allows for the seven TLPs and 2 DLLPs placed in FIG.16B to be placed more compactly—they fit in five fewer DWs and allow forplacement of an eighth TLP.

FIG. 17 shows a table of PCIe 5.0 TLP efficiencies. Table 1700 shows howTLP efficiency under the most current version of the PCIe protocolvaries with transaction size, yielding efficiencies above 90% for largepayloads but dropping down to 62.7% for header-only transactions. Theseefficiencies are the same regardless of link width. Table 1500 in FIG.15 shows flit-based packetization achieving TLP efficiencies rangingfrom 88.9%-94.4% across link widths, a relatively uniform efficiency ascompared to the range of TLP efficiencies in PCIe 5.0 across transactionsizes.

FIG. 18A illustrates an exemplary pair of protocol stacks implemented ina transmitting-receiving device pair. Protocol stacks 1800 and 1804 canbe any kind of protocol or network stack, such as a PCIe stack. Althoughreferences are made herein to a PCIe stack, the same concepts may beapplied to other protocol or network stacks. In one embodiment, protocolstack 1800 is a PCIe protocol stack comprising transaction layer 1810,data link layer 1820, and physical layer 1830. A communication port maybe referred to as a module, circuitry, interface, or port implementingor including protocol stack 1800 or any other protocol stack. Thus, inone embodiment, a protocol stack can comprise a transaction layermodule, a data link layer module and a physical layer module. Such aprotocol stack can also be considered as comprising transaction layercircuitry, data link layer circuitry, and physical layer circuitry. Whenreferencing the protocol stack as a whole, a protocol stack can bereferred to as protocol stack circuitry or a protocol stack module.

PCI Express uses packets to communicate information between a rootcomplex, switches, and endpoints. For example, information to be sentfrom transmitting device 1840 to receiving device 1850 is sent fromprocessor 1860 (or any other processing device of transmitting device1840) to protocol stack 1800. Transaction layer 1810 packets carry theinformation to be delivered from processor 1860 of transmitting device1840 to processor 1894 of receiving device 1850. As the packets that areformed at transaction layer 1810 move down the protocol stack to datalink layer 1820 and then to physical layer 1830, they are extended withinformation to handle packets at those layers. Physical layer 1830 oftransmitting device 1840 transmits packets over link 1854 to physicallayer 1870 of receiving device 1850. There, the reverse process occurs,and the information added to the packets as they moved down protocolstack 1800 are stripped as they move up protocol stack 1804. Transactionlayer 1890 of protocol stack 1874 delivers the payload of the packetssent from transmitting device 1840 to processor 1894 of receiving device1850, thus resulting a message being sent from transmitting device 1840to receiving device 1850.

In one embodiment, transaction layer 1810 provides an interface forprocessor 1860 to PCIe protocol stock 1800. Transaction layer 1810 isresponsible for the assembly and disassembly of transaction layerpackets (TLPs) that deliver information between devices. Upon receipt ofinformation from processor 1860, transaction layer 1810 assembles one ormore TLP packets that will deliver the information to receiving device1850. TLP packet 1842 is one embodiment of a TLP packet. TLP packet 1842comprises TLP header 1844 and payload 1846. Additional information canbe included in a TLP packet, such as an end-to-end cyclic redundancycode (ECRC), an error-detection code that a PCIe transaction layer cancalculate for a TLP packet.

Data link layer 1820 acts as an intermediate stage between transactionlayer 1810 and physical layer 1830. In one embodiment, oneresponsibility of data link layer 1820 is to provide a reliablemechanism for exchanging Transaction Layer Packets (TLPs) betweendevices across a link. In one embodiment, the reliability mechanism isimplemented in part by determining a packet sequence number for a TLPpacket and calculating a link CRC (LCRC) value based on the contents ofthe TLP packet and the packet's sequence number. Data link layer 1820appends information 1852 to the head of TLP packet 1842 that includesthe packet sequence number and appends LCRC value 1856 to the tail ofTLP packet 1842. Data link layer 1820 submits TLP 1842 with appendedinformation to physical layer 1830 for transmission across link 1854 toreceiving device 1850.

Moving down the protocol stack 1800 of transmitting device 1840, in oneembodiment, physical layer 1830 includes logical sub-layer 1832 andelectrical sub-layer 1834 to physically transmit a packet to an externaldevice. Here, logical sub-layer 1832 is responsible for the “digital”functions of physical layer 1830. In this regard, the logical sub-layerincludes a transmit section to prepare outgoing information fortransmission by physical sub-layer 1834, and a receive section toidentify and prepare received information before passing it to data linklayer 1820. Logical sub-layer 1832 frames the appended TLP packet withstart transaction packet (STP) field 1866 to generate an as-transmittedTLP 1868 that is transmitted across link 1854. The STP field 1866comprises sequence number 1852, frame CRC bits, the length of the TLP,and other information.

As used herein, the term “transaction layer packet” refers to TLPsgenerated by transaction layer 1810 and comprises TLP header and payloadinformation. The terms “transaction layer packet information” and“transaction layer packet data” can refer to either the TLP header, theTLP payload, or both. As used herein, the term “transaction layerpacket” does not include information added to a TLP, such as sequencenumber, LCRC, or framing data added by the data link and physicallayers, unless expressly stated. Similarly, the term “data link layerpacket” refers to data link layer packets that do not contain framingdata added by a physical layer, unless expressly stated.

Electrical sub-layer 1834 includes transmitter 1836 and receiver 1838.Transmitter 1836 is supplied symbols by logical sub-layer 1832, whichtransmitter 1836 serializes and transmits to receiving device 1850across link 1854. Receiver 1838 is supplied with received serializedsymbols sent across link 1854 by receiving device 1850 and transformsthe received signals into a bitstream. The bitstream is deserialized andsupplied to logical sub-layer 1832. In one embodiment, packets aretransmitted across link 1854 using an 8b/10b data encoding scheme,wherein eight bits of data are transmitted as ten-bit symbols.

Although transaction layer 1810, data link layer 1820, and physicallayer 1830 are discussed in reference to an embodiment of a PCIeprotocol stack, a protocol stack is not so limited. In otherembodiments, protocol stack 1800 can have different layers and/or feweror more layers than those shown. Further, in other embodiments, theseparate layers shown in FIG. 18A can be combined into a single layer,and a single layer as shown in FIG. 18A can be split into multiplelayers. Any of the layers in the protocol stack shown in FIG. 18A can beimplemented as part of the operating system of a computing device, oneor more software applications independent of the operating system, oroperate at another software layer. The layers shown in FIG. 18A can beimplemented in software, hardware, firmware or combinations thereof andcan be alternately referred to as modules or circuitry (e.g., “data linklayer module,” “physical layer circuitry”) or a combination thereof. Acomputer device referred to as being programmed to perform a method canbe programmed to perform the method via software, hardware, firmware orcombinations thereof.

The Physical Layer can originate physical layer packets (PLP) from atransmitter device and terminates at the Physical Layer of a receiverdevice. PLPs can include EIOS, EIEOS, SKP OS, and other ordered sets.

FIG. 18B is a schematic diagram of an example PHY 1830 and 1970 thatincludes logical elements for encoding and decoding ordered sets inaccordance with embodiments of the present disclosure. Physical layer1830 can include a logical sub-layer 1832 that includes an ordered setencoder logic 1902. Ordered set encoder logic 1902 can includeelectrical circuitry, state machines, and/or other logic to encodepackets with ordered sets, as described above. The ordered set encoderlogic 1902 can include a common logic, circuitry, state machine, etc.for encoding the various types of ordered sets. In some embodiments,each type of OS can be encoded using a corresponding encoding logic. Forexample, SKP OS can be encoded using SKP OS encoding logic 1904, EIOScan be encoded using EIOS OS encoding logic 1906, EIEOS can be encodedusing EIEOS encoding logic 1908, training symbol OS can be encoded usingTSOS 1910, etc.

Data blocks can be encoded with SKP ordered sets, EIOS, EIEOS, training(TS1/TS2) ordered sets, SKP end ordered sets, or other types of orderedsets. The OS encoding logic 1912 can encode any type of OS into a datablock, in which case a common state machine can be used by to performthe encoding of the data block. In some embodiments, each type of OS canbe encoded by a corresponding encoding logic, e.g., making use of aunique state machine. A combination of a common encoder and specific OSencoder can also be used.

The OS encoding logic 1902 can also include a shift register, such aslinear-function shift register (LFSR) 1912. The LFSR 1912 can beembodied using logic circuitry, such as circuitry that includesexclusive or (XOR) gates or other circuitry. The LFSR 1912 can be usedto check bits after encoding the packet and prior to sending the encodedbits out to the PHY.

The receiving device 1850 can include a physical layer 1870 that alsoincludes a logical sublayer 1872. Logical sublayer 1872 includes an OSdecoder logic 1922. OS decoder logic 1922 can decode OS bits from areceived packet. The OS decoder 1922 can include a common state machine(and/or other logic) for decoding the OS bits from the received packet.In some embodiments, each type of OS can be decoded by a correspondingdecoder logic. For example, SKP OS can be decoded using SKP OS decodinglogic 1924, EIOS can be decoded using EIOS OS decoding logic 1926, EIEOScan be decoded using EIEOS decoding logic 1928, training symbol OS canbe decoded using TSOS 1930, etc.

The OS decoding logic 1922 can also include a shift register, such aslinear-function shift register (LFSR) 1932. The LFSR 1932 can beembodied using logic circuitry, such as circuitry that includesexclusive or (XOR) gates or other circuitry. LFSR 1932 can be used tocheck the OS bits received in a packet against expected bits fortransmission errors. For example, when checking that 5 out of 8 SKP OSbits are accurate against the expected bits during a certain interval,the LFSR 1932 can be used to determine whether bit errors have occurredin the received packet.

While this disclosure has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present disclosure.

A design may go through various stages, from creation to simulation tofabrication. Data representing a design may represent the design in anumber of manners. First, as is useful in simulations, the hardware maybe represented using a hardware description language or anotherfunctional description language. Additionally, a circuit level modelwith logic and/or transistor gates may be produced at some stages of thedesign process. Furthermore, most designs, at some stage, reach a levelof data representing the physical placement of various devices in thehardware model. In the case where conventional semiconductor fabricationtechniques are used, the data representing the hardware model may be thedata specifying the presence or absence of various features on differentmask layers for masks used to produce the integrated circuit. In anyrepresentation of the design, the data may be stored in any form of amachine readable medium. A memory or a magnetic or optical storage suchas a disc may be the machine readable medium to store informationtransmitted via optical or electrical wave modulated or otherwisegenerated to transmit such information. When an electrical carrier waveindicating or carrying the code or design is transmitted, to the extentthat copying, buffering, or re-transmission of the electrical signal isperformed, a new copy is made. Thus, a communication provider or anetwork provider may store on a tangible, machine-readable medium, atleast temporarily, an article, such as information encoded into acarrier wave, embodying techniques of embodiments of the presentdisclosure.

A module as used herein refers to any combination of hardware, software,and/or firmware. As an example, a module includes hardware, such as amicro-controller, associated with a non-transitory medium to store codeadapted to be executed by the micro-controller. Therefore, reference toa module, in one embodiment, refers to the hardware, which isspecifically configured to recognize and/or execute the code to be heldon a non-transitory medium. Furthermore, in another embodiment, use of amodule refers to the non-transitory medium including the code, which isspecifically adapted to be executed by the microcontroller to performpredetermined operations. And as can be inferred, in yet anotherembodiment, the term module (in this example) may refer to thecombination of the microcontroller and the non-transitory medium. Oftenmodule boundaries that are illustrated as separate commonly vary andpotentially overlap. For example, a first and a second module may sharehardware, software, firmware, or a combination thereof, whilepotentially retaining some independent hardware, software, or firmware.In one embodiment, use of the term logic includes hardware, such astransistors, registers, or other hardware, such as programmable logicdevices.

Use of the phrase “to” or “configured to,” in one embodiment, refers toarranging, putting together, manufacturing, offering to sell, importingand/or designing an apparatus, hardware, logic, or element to perform adesignated or determined task. In this example, an apparatus or elementthereof that is not operating is still ‘configured to’ perform adesignated task if it is designed, coupled, and/or interconnected toperform said designated task. As a purely illustrative example, a logicgate may provide a 0 or a 1 during operation. But a logic gate‘configured to’ provide an enable signal to a clock does not includeevery potential logic gate that may provide a 1 or 0. Instead, the logicgate is one coupled in some manner that during operation the 1 or 0output is to enable the clock. Note once again that use of the term‘configured to’ does not require operation, but instead focus on thelatent state of an apparatus, hardware, and/or element, where in thelatent state the apparatus, hardware, and/or element is designed toperform a particular task when the apparatus, hardware, and/or elementis operating.

Furthermore, use of the phrases ‘capable of/to,’ and or ‘operable to,’in one embodiment, refers to some apparatus, logic, hardware, and/orelement designed in such a way to enable use of the apparatus, logic,hardware, and/or element in a specified manner. Note as above that useof to, capable to, or operable to, in one embodiment, refers to thelatent state of an apparatus, logic, hardware, and/or element, where theapparatus, logic, hardware, and/or element is not operating but isdesigned in such a manner to enable use of an apparatus in a specifiedmanner.

A value, as used herein, includes any known representation of a number,a state, a logical state, or a binary logical state. Often, the use oflogic levels, logic values, or logical values is also referred to as 1'sand 0's, which simply represents binary logic states. For example, a 1refers to a high logic level and 0 refers to a low logic level. In oneembodiment, a storage cell, such as a transistor or flash cell, may becapable of holding a single logical value or multiple logical values.However, other representations of values in computer systems have beenused. For example the decimal number ten may also be represented as abinary value of 1010 and a hexadecimal letter A. Therefore, a valueincludes any representation of information capable of being held in acomputer system.

Moreover, states may be represented by values or portions of values. Asan example, a first value, such as a logical one, may represent adefault or initial state, while a second value, such as a logical zero,may represent a non-default state. In addition, the terms reset and set,in one embodiment, refer to a default and an updated value or state,respectively. For example, a default value potentially includes a highlogical value, i.e. reset, while an updated value potentially includes alow logical value, i.e. set. Note that any combination of values may beutilized to represent any number of states.

The embodiments of methods, hardware, software, firmware or code setforth above may be implemented via instructions or code stored on amachine-accessible, machine readable, computer accessible, or computerreadable medium which are executable by a processing element. Anon-transitory machine-accessible/readable medium includes any mechanismthat provides (i.e., stores and/or transmits) information in a formreadable by a machine, such as a computer or electronic system. Forexample, a non-transitory machine-accessible medium includesrandom-access memory (RAM), such as static RAM (SRAM) or dynamic RAM(DRAM); ROM; magnetic or optical storage medium; flash memory devices;electrical storage devices; optical storage devices; acoustical storagedevices; other form of storage devices for holding information receivedfrom transitory (propagated) signals (e.g., carrier waves, infraredsignals, digital signals); etc., which are to be distinguished from thenon-transitory mediums that may receive information there from.

Instructions used to program logic to perform embodiments of thedisclosure may be stored within a memory in the system, such as DRAM,cache, flash memory, or other storage. Furthermore, the instructions canbe distributed via a network or by way of other computer readable media.Thus a machine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer), but is not limited to, floppy diskettes, optical disks,Compact Disc, Read-Only Memory (CD-ROMs), and magneto-optical disks,Read-Only Memory (ROMs), Random Access Memory (RAM), ErasableProgrammable Read-Only Memory (EPROM), Electrically ErasableProgrammable Read-Only Memory (EEPROM), magnetic or optical cards, flashmemory, or a tangible, machine-readable storage used in the transmissionof information over the Internet via electrical, optical, acoustical orother forms of propagated signals (e.g., carrier waves, infraredsignals, digital signals, etc.). Accordingly, the computer-readablemedium includes any type of tangible machine-readable medium suitablefor storing or transmitting electronic instructions or information in aform readable by a machine (e.g., a computer).

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present disclosure. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

In the foregoing specification, a detailed description has been givenwith reference to specific exemplary embodiments. It will, however, beevident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the disclosure asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense. Furthermore, the foregoing use of embodiment andother exemplarily language does not necessarily refer to the sameembodiment or the same example, but may refer to different and distinctembodiments, as well as potentially the same embodiment.

The foregoing description of one or more implementations providesillustration and description, but is not intended to be exhaustive or tolimit the scope of embodiments to the precise form disclosed.Modifications and variations are possible in light of the aboveteachings or may be acquired from practice of various embodiments.

Example 1 is an apparatus comprising a port for transmitting data; and alink coupled to the port. The port comprising a physical layer device(PHY) to decode a physical layer packet, the physical layer packetreceived across the link, the physical layer packet including a firstbit sequence corresponding to a first ordered set, and a second bitsequence corresponding to a second ordered set, the first bit sequenceimmediately adjacent to the second bit sequence.

Example 2 may include the subject matter of example 1, wherein the firstordered set is received at a predetermined ordered set interval.

Example 3 may include the subject matter of example 2, wherein thepredetermined ordered set interval occurs following a flow control unit(flit).

Example 4 may include the subject matter of example 3, wherein thepredetermined ordered set interval occurs between two flits.

Example 5 may include the subject matter of any of examples 1-4, whereinthe first ordered set comprises eight bytes and the second ordered setcomprises eight bytes.

Example 6 may include the subject matter of example 5, the port to readthe eight bytes of the first ordered set; and check that five of theeight bytes match an expected type of ordered set.

Example 7 may include the subject matter of any of examples 1-6, theport to determine that five of the eight bytes do not match an expectedtype of ordered set; and enter a link recovery state.

Example 8 may include the subject matter of any of examples 1-6, theport to determine that five of the eight bytes match an electrical idleordered set (EIOS); and enter a low power state after the second orderedset.

Example 9 may include the subject matter of any of examples 1-6, theport to determine that five of the eight bytes match an electrical idleexit ordered set (EIEOS); and enter a link recovery state after thesecond ordered set.

Example 10 may include the subject matter of any of examples 1-6, theport to determine that five of the eight bytes match a skip ordered set(SKP OS); read the second ordered set; and determine an ordered set typefrom the second ordered set.

Example 11 may include the subject matter of example 10, the port todetermine that the second ordered set matches a skip end ordered set(SKP_END OS); identify a next eight bytes following the SKP_END OS asPHY payload; identify a next eight bytes following the PHY payload as areplicated PHY payload; and determine that a data stream follows the PHYpayload that follows the SKP_END OS.

Example 12 may include the subject matter of example 10 10, the port todetermine that the second ordered set matches a SKP OS; continue tocheck bytes following the second ordered set for SKP OS; determine thatmore than 56 bytes comprise a SKP OS; and cause the link to enterrecovery.

Example 13 may include the subject matter of example 10, the port todetermine that the second ordered set matches a SKP OS; determine thatfive of eight bytes following the second ordered set matches a skip endordered set (SKP_END OS); and identify a next eight bytes following theSKP_END OS as PHY payload; and determine that a data stream follows thePHY payload that follows the SKP_END OS.

Example 14 may include the subject matter of example 13, the port toidentify a next eight bytes following the PHY payload as a replicatedPHY payload.

Example 15 may include the subject matter of example 1, wherein thefirst ordered set comprises eight bytes and the second ordered setcomprises eight bytes, the first and second ordered sets comprisingelectrical idle exit ordered sets (EIEOS); the port to receive twoadditional EIEOS; receive thirty two training sequence ordered sets forlink training.

Example 16 may include the subject matter of example 15, wherein each ofthe training sequence ordered sets comprises a first portion and asecond portion, the first portion comprising eight symbols and thesecond portion comprising eight symbols, each symbol comprising onebyte, the first portion comprising identical information in each symbolas the second portion.

Example 17 is a method comprising receiving, at a port, a first bitsequence corresponding to a first ordered set comprising eight bytes;receiving, at the port, a second bit sequence corresponding to a secondordered set comprising eight bytes, the first bit sequence immediatelyadjacent to the second bit sequence, the first ordered set identical tothe second ordered set; comparing a portion of the first ordered setagainst an expected ordered set; and determining a type of ordered setbased on the comparison.

Example 18 may include the subject matter of example 17, whereinreceiving the first bit sequence comprises receiving the first bitsequence at a predetermined ordered set interval.

Example 19 may include the subject matter of example 18, wherein thepredetermined ordered set interval occurs following a flow control unit(flit).

Example 20 may include the subject matter of examples 17-19, furthercomprising reading, by the port, the eight bytes of the first orderedset; and checking that five of the eight bytes match an expected type ofordered set.

Example 21 may include the subject matter of example 20, furthercomprising determining that five of the eight bytes do not match anexpected type of ordered set; and entering a link recovery state.

Example 22 may include the subject matter of example 20, the port todetermining that five of the eight bytes match an electrical idleordered set (EIOS); and entering a low power state after the secondordered set.

Example 23 may include the subject matter of example 20, the port todetermining that five of the eight bytes match an electrical idle exitordered set (EIEOS); and entering a link recovery state after the secondordered set.

Example 24 may include the subject matter of example 20, the port todetermining that five of the eight bytes match a skip ordered set (SKPOS); reading the second ordered set; and determining an ordered set typefrom the second ordered set.

Example 25 may include the subject matter of example 24, the port todetermining that the second ordered set matches a skip end ordered set(SKP_END OS); identifying a next eight bytes following the SKP_END OS asPHY payload; identifying a next eight bytes following the PHY payload asa replicated PHY payload; and determining that a data stream follows thePHY payload that follows the SKP_END OS.

Example 26 may include the subject matter of example 24, the port todetermining that the second ordered set matches a SKP OS; continuing tocheck bytes following the second ordered set for SKP OS; determiningthat more than 56 bytes comprise a SKP OS; and causing the link to enterrecovery.

Example 27 may include the subject matter of example 24, the port todetermining that the second ordered set matches a SKP OS; determiningthat five of eight bytes following the second ordered set matches a skipend ordered set (SKP_END OS); and identifying a next eight bytesfollowing the SKP_END OS as PHY payload; determining that a data streamfollows the PHY payload that follows the SKP_END OS.

Example 28 may include the subject matter of example 17, wherein thefirst ordered set comprises eight bytes and the second ordered setcomprises eight bytes, the first and second ordered sets comprisingelectrical idle exit ordered sets (EIEOS); the method further comprisingreceiving two additional EIEOS; receiving thirty two training sequenceordered sets for link training; wherein each of the training sequenceordered sets comprises a first portion and a second portion, the firstportion comprising eight symbols and the second portion comprising eightsymbols, each symbol comprising one byte, the first portion comprisingidentical information in each symbol as the second portion.

Example 29 is a system comprising a host device comprising a downstreamport; a link partner comprising an upstream port; a link interconnectingthe downstream port with the upstream port. The downstream port totransmit, during a predetermined interval, a first set of eight bytescomprising a first ordered set and a second set of eight bytescomprising a second ordered set, the first ordered set identical to thesecond ordered set. The upstream port to receive the first set of eightbytes; determine that the first set of eight bytes were received duringan expected ordered set interval; and identify an ordered set type basedon the first set of eight bytes.

Example 30 may include the subject matter of example 29, wherein thefirst ordered set is received at a predetermined ordered set interval.

Example 31 may include the subject matter of example 30, wherein thepredetermined ordered set interval occurs following a flow control unit(flit).

Example 32 may include the subject matter of example 31, wherein thepredetermined ordered set interval occurs between two flits.

Example 33 may include the subject matter of any of examples 29-32, theupstream port to determine that five of the eight bytes do not match anexpected type of ordered set; and enter a link recovery state.

Example 34 may include the subject matter of any of examples 29-32, theupstream port to determine that five of the eight bytes match anelectrical idle ordered set (EIOS); and enter a low power state afterthe second ordered set.

Example 35 may include the subject matter of any of examples 29-32, theupstream port to determine that five of the eight bytes match anelectrical idle exit ordered set (EIEOS); and enter a link recoverystate after the second ordered set.

Example 36 may include the subject matter of any of examples 29-32, theupstream port to determine that five of the eight bytes match a skipordered set (SKP OS); read the second ordered set; and determine anordered set type from the second ordered set.

Example 37 may include the subject matter of example 36, the upstreamport to determine that the second ordered set matches a skip end orderedset (SKP_END OS); identify a next eight bytes following the SKP_END OSas PHY payload; identify a next eight bytes following the PHY payload asa replicated PHY payload; and determine that a data stream follows thePHY payload that follows the SKP_END OS.

Example 38 may include the subject matter of example 36, the upstreamport to determine that the second ordered set matches a SKP OS; continueto check bytes following the second ordered set for SKP OS; determinethat more than 56 bytes comprise a SKP OS; and cause the link to enterrecovery.

Example 39 may include the subject matter of example 29, wherein thefirst ordered set comprises eight bytes and the second ordered setcomprises eight bytes, the first and second ordered sets comprisingelectrical idle exit ordered sets (EIEOS); the upstream port to receivetwo additional EIEOS; receive thirty two training sequence ordered setsfor link training.

Example 40 may include the subject matter of example 39, wherein each ofthe training sequence ordered sets comprises a first portion and asecond portion, the first portion comprising eight symbols and thesecond portion comprising eight symbols, each symbol comprising onebyte, the first portion comprising identical information in each symbolas the second portion.

What is claimed is:
 1. An apparatus comprising: a receiver comprising aport, the port comprising physical layer circuitry (PHY), the PHY to:receive, during a SKIP Ordered Set (SKP OS) interval, an ordered set(OS) from a link; wherein the received OS comprises a first eight bytesand a second eight bytes; and determine, based on the first eight bytesof the received OS, whether the received OS is a SKP OS, an electricalidle OS (EIOS), or an electrical idle exit OS (EIEOS).
 2. The apparatusof claim 1, the PHY to determine the type of OS when at least 5 bytes ofthe first eight bytes match one type of OS.
 3. The apparatus of claim 1,the PHY to determine that the received OS comprises a SKP OS when atleast five bytes of the first eight bytes of the received OS correspondto expected bytes for a SKP OS.
 4. The apparatus of claim 3, the PHY to:read a second eight bytes of the received OS; determine that the secondeight bytes of the received OS match a SKP_END OS when at least 5 bytesof the second eight bytes of the received OS match a SKP_END OS; andprocess a PHY payload that follows the SKP_END OS.
 5. The apparatus ofclaim 1, the PHY to: determine that the received OS comprises an EIOSwhen at least five bytes of the first eight bytes corresponding to bytesfor an EIOS; and cause the link to prepare to enter a low power state.6. The apparatus of claim 1, the PHY to: determine that the received OScomprises an EIEOS when at least five bytes of the first eight bytescorresponding to bytes for an EIEOS; and cause the link to enterrecovery.
 7. The apparatus of claim 1, the PHY to: read a second eightbytes of the received OS; determine that at least five bytes of thesecond eight bytes do not match any type of OS; and cause the link toenter recovery.
 8. The apparatus of claim 1, wherein the received OScomprises at least 16 bytes.
 9. The apparatus of claim 1, wherein SKP OSinterval occurs at a flit boundary.
 10. The apparatus of claim 1,wherein the SKP OS interval occurs after every 74 flits in SRIS mode.11. The apparatus of claim 1, wherein the SKP OS interval occurs afterabout 740 flits in common clock or SRNS mode.
 12. The apparatus of claim1, the PHY to: receive a PHY payload after receiving the OS; anddetermine a payload type from a PHY payload type field, the payload typecomprising one of a margin payload or a linear feedback shift register.13. The apparatus of claim 1, the PHY to determine that the received OSis valid when at least five bytes of the first eight bytes correspondingto an expected value for a type of OS.
 14. The apparatus of claim 1, thePHY to: receive a training sequence ordered set, the training sequenceordered set comprising a first eight bytes and a second eight bytes;perform a parity check of one of the first eight bytes or the secondeight bytes of the training sequence ordered set; and determine that thetraining sequence ordered set is valid when the first eight bytes or thesecond eight bytes passing the parity check.
 15. The apparatus of claim1, the PHY to: receive a start data stream ordered set; checkingE1_87_87_87 sets in the start data stream ordered set; and determinethat the start data stream ordered set is valid if four E1_87_87_87 setsare valid.
 16. A method comprising: receiving, during a SKIP Ordered Set(SKP OS) interval, an ordered set (OS) from across a link; reading afirst eight bytes of the received OS; and determining, based on thefirst eight bytes of the received OS, whether the received OS is a SKPOS, an electrical idle OS (EIOS), or an electrical idle exit OS (EIEOS).17. The method of claim 16, further comprising determining the type ofOS when at least 5 bytes of the first eight bytes match one type of OS.18. The method of claim 16, further comprising determining that thereceive OS comprises a SKP OS when at least five bytes of the firsteight bytes of the received OS correspond to expected bytes for a SKPOS.
 19. The method of claim 18, further comprising: reading a secondeight bytes of the received OS; determining that the second eight bytesof the received OS match a SKP_END OS when at least 5 bytes of thesecond eight bytes of the received OS matching a SKP_END OS; andprocessing a PHY payload that follows the SKP_END OS.
 20. The method ofclaim 16, further comprising: determining that the received OS comprisesan EIOS when at least five bytes of the first eight bytes correspondingto bytes for an EIOS; and cause the link to prepare to enter a low powerstate.
 21. The method of claim 16, further comprising: determining thatthe received OS comprises an EIEOS when at least five bytes of the firsteight bytes corresponding to bytes for an EIEOS; and causing the link toenter recovery.
 22. The method of claim 16, further comprising: readinga second eight bytes of the received OS; determining that at least fivebytes of the second eight bytes do not match any type of OS; and causingthe link to enter recovery.
 23. The method of claim 16, wherein thereceived OS comprises at least 16 bytes.
 24. The method of claim 16,wherein SKP OS interval occurs at a flit boundary.
 25. The method ofclaim 16, wherein the SKP OS interval occurs after every 74 flits inSRIS mode.
 26. The method of claim 16, wherein the SKP OS intervaloccurs after about 740 flits in common clock or SRNS mode.
 27. Themethod of claim 16, further comprising: receiving a PHY payload afterreceiving the OS; and determining a payload type from a PHY payload typefield, the payload type comprising one of a margin payload or a linearfeedback shift register.
 28. The method of claim 16, further comprisingdetermining that the received OS is valid when at least five bytes ofthe first eight bytes corresponding to an expected value for a type ofOS.
 29. The method of claim 16, further comprising: receiving a trainingsequence ordered set, the training sequence ordered set comprising afirst eight bytes and a second eight bytes; performing a parity check ofone of the first eight bytes or the second eight bytes of the trainingsequence ordered set; and determining that the training sequence orderedset is valid when the first eight bytes or the second eight bytespassing the parity check.
 30. The method of claim 16, furthercomprising: receiving a start data stream ordered set; checkingE1_87_87_87 sets in the start data stream ordered set; and determiningthat the start data stream ordered set is valid if four E1_87_87_87 setsare valid.
 31. A system comprising: a first device; a second device; thesecond device coupled to the first device by a link, wherein the linkcomprises multiple physical lanes; the first device comprising protocolstack circuitry to send an ordered set comprising a first eight bytesand a second eight bytes to the second device; the second devicecomprising protocol stack circuitry to: receive, during a SKIP OrderedSet (SKP OS) interval, an ordered set (OS) from across a link; read afirst eight bytes of the received OS; and determine, based on the firsteight bytes of the received OS, whether the received OS is a SKP OS, anelectrical idle OS (EIOS), or an electrical idle exit OS (EIEOS). 32.The system of claim 31, the second device to determine the type of OSwhen at least 5 bytes of the first eight bytes match one type of OS. 33.The system of claim 31, the second device to determine that the receivedOS comprises a SKP OS when at least five bytes of the first eight bytesof the received OS correspond to expected bytes for a SKP OS.
 34. Thesystem of claim 33, the second device to: read a second eight bytes ofthe received OS; determine that the second eight bytes of the receivedOS match a SKP_END OS when at least 5 bytes of the second eight bytes ofthe received OS matching a SKP_END OS; and process a PHY payload thatfollows the SKP_END OS.